I've had one for 13 months and it's been extremely useful. If I don't want to talk to someone or don't want to answer the phone, I either ignore the call or turn off the ringer/vibrate-feature (no way I was calling it a vibrator!) - that doesn't happen too frequently though. My phone makes things much easier and provides more flexibility for making plans, changing plans, etc. It's also nice for calling home to give my parents an update on where I am and what I'm doing...and that I'm alive so they don't get worried. That is more for their sake than mine though.
Free long distance is nice too because my sisters are older and in two different states. While I actively had a computer business for a few months (I've gotten too busy with school and other things now though) I put my cell phone number at the business number and this made things extremely easy.
All in all, I'm a big fan of the cell phone. However, not my cell phone, the Nokia 3360, it's been doing funky stuff and the battery life is crap now, so I'll be getting a new phone before I go off to college.