Shifting. This has been my biggest issue with my bike, and it turns out to be the easiest to adjust. On my 3 spd it just means screwing a chain tighter or looser. Hey, I can do that! Now it shifts like butter. Also, I got my hands nice and greasy for the first time in class, like a proper mechanical person. Of course, this was only from poking around the dirty dirty wheels while replacing broken reflectors, which really shouldn't count.
Ooh, if you haven't heard the news yet, google maps offers biking directions now! Score!!