Just throwing in my own experience, but...
I used to work for a small web development company of around 15 people. Starting there was fun, I was able to work with Perl, PHP, and some other things that I really enjoyed, including almost 100% of my work being done on a Unix platform of some kind. However, as time wore on, things started building up that I just could not live with. For one, my boss had originally described to me his "vision" of a network setup that I thought would be really great to implement. Unfortunately, he ended up changing his mind, and went pretty much from pro-Unix to pro-NT (something I am not). The plan then became to move as much away from the Sun servers we had to NT servers with Exchange for our customers. We'd be going from PHP and Perl to ASP. That coupled with the fact that a client thought me to be incompetent due to mistakes that my boss made BEFORE I even started working there pretty much made up my mind.
I now see where people who say "Just quit" are coming from, but I believe that when they say that, there is more to it, like "Start looking for another job now" or "Make job satisfaction how you can". After all that, I found another job making more than twice what I was making before, and I am definitely doing more that I enjoy here. It was hard to take the job though because it involved moving away from a LOT, but it's a year contract, and I'm young so that year's experience will be worth a heck of a lot in the long run.
Bottom line I guess is if you are unhappy then don't just sit there... brush off your resume and go looking. You don't have to quit without any opportunities in front of you, just don't whine about how bad it is, and then do nothing about it. :-)
