I don't think anyone MUST have a laptop (unless, of course the school requires it), but it is probably nice, especially with all this new wireless stuff going up. Most schools probably have enough computers that it wouldn't be a big issue, I would assume. Still, having a laptop is more convenient.
As for the whole PC vs. Mac thing, I had a PC laptop for the first 3.5 years of undergrad. The hardware was alright (although the HD had to be replaced once, but it is still a consumer electronic), the problem was in Windows. It came with Windows ME, which was pretty bad, but it still ran decent. Then, I upgraded to XP, and it was alright, but then it started to have problems. I got all kinds of spyware on my computer. I didn't use kazaa, only internet explorer. Things would install on my computer without me knowing. Weird. My sisters tech wizard boyfriend spent like two hours getting that stuff fixed. In the mean time, anytime I tried to use my MP3 player, it made me reinstall the drivers (talk about a pain) and it had a bunch of other problems. XP wouldn't communicate with my CD drive, so I couldn't install anyting new after a while. Then, the harddrive failed again......so I decided to get something new.
Given all the recent viruses and stuff for Windows, I looked into Apple. I really liked their powerbook series, so I got a 12" one. I had never used a Mac before, so it was a new experience. Its worked very well.....I have never had a crash or an incompatability problem with Windows (I transfer files daily between the two). The computer is real fast and gets real good battery life.
One of the cool things that I did not know about when I bought my computer is a feature on OS X.3 called expose. Basically, it allows you to view all the screens you have open at once and switch between them. So, if you have 10 different windows open, you press a button (which I have mapped to my mouse) and you can see mini versions of the windows and quickly switch between them. Its so much faster for switching betweens windows its amazing- its actually made me faster on the computer. When I use a PC, it feels to clunky to me to have to switch windows by clicking on the task bar or using alt+tab. You can check it out here, because its kinda hard to explain.
http://www.apple.com/macosx/features/expose/#
Anyways, I was a little nervious about switching to Mac, but in all honestly, its not that much different. Took me about 3 days to get used to. OS X is definitely more stable than XP. To me, it also feels much smoother and easier to use.