I've wanted a Camelbak for a really long time. I finally decided to buy one before I left for Spain. Since getting it, I learned that it's a bear to clean, mostly because it's nearly impossible to dry. Camelbak makes a cleaning kit for their bladders and I bought one from Sunshine Cycles earlier this semester. It comes with a specially shaped bottle brush to clean the bladder, a cool cleaner snake thing that goes through the straw, some anti-bacterial tablets (for heavy cleanings), and a hanger/dryer. It makes cleaning the Camelbak about 50 times easier, which means that I'm more likely to do it. In fact, I give it at least a cursory cleaning and allow it to dry after every use.
If you have a Camelbak and find that it's not so fun to clean, I recommend dropping the money for the cleaning kit.