Should slides in a deck have boring solid colored backgrounds or images/snazzy backgrounds?

Very much depends on 1) your goal, and 2) your audience. If you are speaking at a conference, big visuals and builds can be quite powerful as they are fun / captivating. For big audiences, the message is as important as its delivery. If you are speaking to investors or partners, too much imagery can come across as too much 'fluff'. I read dozens of decks each week - as most investors do - and have seen a trend towards text and product screenshots. I generally believe simpler is better. And I generally like to feel as though more care was put into the content than the colors. Just my two cents!

Solid background, each slide with a picture or graphic  that detracts from the boredom and illustrates the point (can be "jazzy" but not overwhelming). Here's some good advice: http://blog.guykawasaki.com/2005/12/the_102030_rule.html 10/20/30 rule == 10 slides, 20 minutes, 30 point font. Don't make it long, don't talk too much, and don't try to pack every point you are trying to make onto the slide in small print... talk to the main bullets. A bit over the top, but think of Steve Jobs' slides during Apple keynotes.

Don't think so much in terms if the images are too snazzy but rather, do they tell YOUR company story? Are they representative of how the company should be perceived? Would you use one of them maybe in an ad to advertise your company? If the answer is no then they could be distracting from your message or sending the wrong message. It doesn't matter if you have 10 slides or 20 slides if you know how to present the information. It's much better to break down your topics into more slides than to pack a lot of information into a single slide. People ARE visual creatures.  Science says so! Pictures are ~60% more memorable than words alone. Visual appeal subconsciously enhances how people feel about certain things without even realizing. Clean, easy to read  information is easier to process and most people will subconciously perceive it as more likable. When it comes to images, think bold, unique, inspiring. Size them up to fill the slide. Think about how ads are, cleaner, simpler lines. When it comes to charts and graph, think simple, easy to read, and highlight what it is that should be seen in them.

Use subtle backgrounds to avoid overpowering the message that the slide is trying to convey.  (Unless the background is intended to convey the meaning of the slide.)  They don't have to be flat colors, though! Honestly, take a look at Apple's various presentations for some great examples.  Each slide is clear, concise and conveys an exact meaning.  They often make use of subtle gradients to keep the backgrounds from being boring. http://www.apple.com/apple-events/

An investor deck is very different than a product or industry presentation. I question whether anyone has gotten funding with a snazzy deck and weak product, but folks get funded all the time with a strong product and super simple deck style (e.g. default b/w PPT template) or even no deck.