I feel like I did not learn anything out of college. Is it a good idea to go back to university and pursue to learn the things I missed?

Learning is a lifetime activity, and does not necessarily have anything to do with college. On the job learning is unavoidable, especially in tech. Reading periodicals, even in this day of blogs, is still valuable -- IEEE has some great stuff if you're into hardcore engineering, or software engineering academic research. Consider joining IEEE and ACM and attending regional meetings. There has to be IEEE in your country. I'd bet ACM as well. Consider joining IEEE societies. On the business side, both practical and theoretical, there are a number of books that any entrepreneur should be reading. Join user groups. Attend unconferences. Start presenting at them. If they don't exist in your area, start them. Work for and with superstars. Always push your limits. Don't settle. To answer your actual question: college can be part of the equation, but by no means is a return to school dictated for you. I'd like to back, probably for an MBA, maybe for a Masters of Science as well.

It probably is not worth it to go back and learn things you missed. Now, learning new things will always be worthwhile. But you should also ask yourself the following: was not learning anything in college a function of the school you went to being not very good or was it because you weren't a good student?

Pick an open source project that interests you, get some respect from existing contributors, so you become one of them eventually. This will make you good in at least that project. Alternatively (or in parallel) build something yourself even if it is a clone of Digg/Quora/Twitter/etc. Since you end up doing end-to-end development, you will get better at the end of that effort. You can go back to school if you want to do academic research, but there is no match for hands on experience if you want to stay in the industry. Moreover, since you didn't learn much in college in the first place (according to you, no flames) it is unlikely that you will learn anything useful if you go back to college now.

Stanford and MIT have great technical podcast lectures on iTunes, though maybe not graduate level, the material is fresh and up to date. Explore the world of podcasts on iTunes. I have found it to be a wonderful universe of learning new topics in a short amount of time and it's FREE. I've jumped from entrepreneurial lectures to autism research to assistive technology. What a great way to be inspired by adjacent technologies.