If I make $30 per hour working a 40 hour/week job, how much should I consider my time worth in terms of deciding whether or not a task is worthwhile?

First, this IS a useful question to answer for yourself, even though you will not get an exact answer. The reason is that you make time//money tradeoffs every day, and you might as well make them consistently. (Pareto optimal even if not optimal.)   Second, I don't agree with Ed Lau's answer, "break even spending rate," at all. Most of your income goes to cover fixed costs, which his calculation ignores (rent, car, food, etc.) Also as others have pointed out, the opportunity cost is always a marginal cost, not an average cost. However his examples of how to use the number are useful and valid.    Various answers can "bound" your answer. For example, if you have a job where you can work as many hours as you want and earn approximately $X per hour from it, then your answer should be close to $X. If free time is worth a lot more than X to you, you should work less. If it's worth a lot less than X, you should be working more.    Most of us don't have that much flexibility in our main job, but may have side jobs with flexibility. For example at various time's I've worked as a consultant at $Y per hour, where Y >> my average hourly pay. During those months, I did attempt to re-orient my thinking to have a much higher opportunity cost of my time. Psychologically, though, it was hard.   And last, adjust for income taxes.  If you make $60K/year and work 2000 hours per year, then your  earnings per hour are  less than $30. Once you consider FICA and state + Federal income tax at the marginal rate (not the average rate), your take-home pay per extra hour is probably 0.7 * 30 = $21/hour. YMMV since some states have low income tax but high sales tax, or real estate taxes, etc.

The problem in asking the question is that money is not a definite universal value any more so than time is.  "John's" time may be more or less valuable to him or her than "Bob's" time is to "Bob" even in the same "task."  Asking someone else how much your own time is worth is akin to asking someone else how much a gallon of whiskey is worth to you.  I understand what the question is, but in making any decision, humans use very personal economic judgement.  The very principled man who values "making money" less than the very practical man will be more likely to find a greater "value" in contesting the aforementioned fine.  It does not suggest irrationality on the principled individual.  In contesting the fine which may cost him his hourly wage of $30, his action brought a greater satisfaction than what he may have attained by simply paying it and increasing his net worth $25.  In the same respect, a person who finds the greatest satisfaction in leisure would place a higher value on his free time than the man who finds the greatest satisfaction in amassing wealth (all other things being equal).  Money is simply a measurement of value (value of work, value of time, value of consumer goods) and since value is absolutely not universal and changes dramatically from one person to the next depending on endless variables and data, the person asking the question is the only one who can answer it.

Here is a simple calculator (protip: you can leave 5-8 as 0 if you want) :: http://www.businessknowhow.com/manage/timecalc2.htm

(Cost of Living/Month)/(# of hours per Month) = Cost of Living/Hour. Cost of Living/Hour + Potential gain from working ($30/hour in this case) = Opportunity Cost of free time / Hour.

Most of the answers boil down to opportunity cost, don't they? But, really, your non-work time is worth nothing if you aren't spending it on the opportunity. In other words, before getting all quant on this topic, consider if you have projects you want to take on that you can't because you are doing work that is outsourceable. Then use common sense (and Edmond Lau's awesome post) to figure out if you should.

You should consider the $30/hr opportunity cost only if you have no choice but to contest the fine during your work hours because you'll end up losing your $30 contesting the fine. If you contest the fine outside work hours, you lose nothing. So the opportunity cost is Nil, if you have the choice of contesting the fine outside work hours. And if you have no choice but to contest during work hours,  then the opportunity cost is $30 and you will be better off paying the $5 fine.

I read a book many years ago that changed the way I looked at my money and time, titled, Your Money Or Your Life. It posited that we make a lot less per hour than we think, after factoring in all the costs of working.  To determine your true earnings/hr., it advised subtracting all costs and hours you expend in order to do your job.  Examples include gas, car repairs, maintenance, work clothes, commute time, meals away from home, drinks or time spent destressing, gifts, training, day care., cost difference between meals eaten out after work because you're too tired to cook. The book helped me to me to look at what I spend my time and money on. Once you figure out your true wage, you then ask yourself before making a purchase, "is this item worth the minutes of my life it took to earn that money. Although not directly answering your question, the book challenged readers to look at what they mindlessly spend their money on, which in the end comes down to an expenditure of your time.  The authors recommended agressively saving and conservativley investing money and living at least partially on the returns, thereby freeing up more of your time for enjoying life. One caveat.  The book is very preachy, which turned me off, even though I agreed with their political views.  However, it was still very much worth the read.  http://www.thesimpledollar.com/your-money-or-your-life-final-reflections/

Sorry to say it but in my opinion your model is wrong. The value per hour is relative and cannot be seen as a fixed amount of money per hour. This is all an economic bogus factor. Let's think about some scenarios. Scenario one: you got two jobs. One is paid 120 and other 30 per hour. How you calculate? The bigger one, because you know you can make 120 or an average? Eh? Scenario one and a half: you start being paid starting from now 45 per hour. How much is your time worth as is the same time and same you as yesterday? Scenario two: you are somewhere in countryside fishing with children or nephews and you can do this only twice a year. You been to come back to work. When you choose do you think at this time as 30/hour or invaluable. So, economically speaking you are right but from happiness point of view you are wrong. As a potentiality you time is much much more worthy than the amount that you are paid. You are only accepting that amount as being fair because everyone usually undervalue himself/herself.

This is the type of relevant questions we start to ask ourselves in this age of hyper potentiality. Every second that we have ticking away steadily can be used in seemingly countless activities. To me, the focus of the question should not be $, but time itself. This one life that you have, what are you going to dedicate it for? From there, you break it down to your long-term, short-term goals, and then identify the activities and learnings required to get there. Factor in the amount of time needed to relax and unwind that is actually counter-intuitively will get you accomplish your goals easier and faster. After you have done all these, everything else you have to "outsource" by throwing money as much as possible to any issues or problems that stand in the way. Here, for every person the answer varies from person to person because of variances in available discretionary income to "waste".