I have a Sidekick III... it's just awesome. Granted I do have a computer, I love being able to IM people or check my e-mail or surf the net when I'm at work (I'm a bartender). The cool things that the III has over the II is its Bluetooth capabilities and more importantly the built-in MP3 player and memory card. I can now go to the gym with just one thing, my cell phone. No longer do I need to carry a cell phone and my MP3 player and worry about the other one getting stolen when I put it where all the bags are. Granted the Sidekicks are a bit larger than regular phones, it's not like you're holding a brick like some people make it seem. And with the display screen flipped out, your cheek actually fits quite well into the open space, unlike when you talk on regular phones, and your cheek makes the screen all sweaty.
The RAZRs were more of a trend, as someone else stated. It is skinny and all, but it's much wider than most phones as a result, about as wide as a deck of cards. I have friends who have gone through several RAZRs since they seem to break so easily. Most of my friends who have those phones like them when they first get them, but a week later, the novelty of having a skinny phone just seems to wear off. I can always use my Sidekick III for fun stuff. I also like to write lyrics and stuff, so I can always just type them up and save them on my phone, which is pretty easy with the qwerty keyboard.