I participated in this year's Toughest Developer Puzzle Ever challenge, and actually managed to finish in the 95th place, which I'm pretty excited about! Solving the puzzles (and there were 100 [*] of them) turned out to be quite challenging, and my head begun to hurt at some point. However, it was well worth the effort; I found it to be a very rewarding experience and I learned a few new things along the way. :)
Many thanks go to the awesome people at woot.com who helped me get unstuck at points where I couldn't move on, even after having tried several different approaches or stared at a problem for extended periods of time. You can find my questions in the dedicated TDPE thread.
I'm really looking forward to next year's puzzles! :D
[*] Well, around 10 levels near the end were freebies, so make that 90. :P