Most Certainly an iBook, for the following reasons:
1. UNIX. Any reputable CS department and any programmer worth his salt punches code in a UNIX environment, and for good reason: It's rock stable, very fast, secure, and portable. If you've learned to use the terminal in OSX, you can use UNIX in the CS lab, and vice versa.
2. Durability. I at one time owned a Dell Inspiron 4150 laptop... and let me tell you, you don't appreciate how nice it is to have a laptop as durable as an iBook until you've had to deal with something less. Between breaking latches, getting dings all over, having a W key stop working, and having the plastic housing on the screen split in half, It went back to Dell many a time. It's not like I abused it either -- kept it in its padded case whenever it moved, and it really didnt move a whole lot, once a week at the most. iBook has no hinges or latches, can get scratched to hell without looking ****ty, and it's also really small and light to carry around.
3. Price. For what you get in an iBook, you can't get a cheap PC that works anywhere near as well. $1000 (with student discount) will get you a decent setup with enough memory to get by, and with a PC, $1000 will get you a slow, slow p4 and 128 megs of RAM.
4. Connectivity. 2 USB, Firewire, Airport are all options, and are all very nice to have. many, many laptop users find themselves having spare Firewire hard drives, and having 2 usb ports is also nice. Most low end pc laptops don't have firewire or even an option for an internal wireless card, and believe me, you don't want to use a PCMIA one, the reception you'll get will be horrid, and the damned thing sticks out of the side of the machine, which is a pain too.
5. Battery. iBooks actually do get about 5 hours on one battery, and the sleep mode actually works -- well. you can close the top, and put it in your backpack, and it'll be fine. If you want to know what happens if you try that with a dell, go look for some pictures.... the screen melts to the keyboard... even if you put it in "standby." My inspiron got about 4 hours of battery life out of TWO batteries.
6. Etc... even beyond coding purposes, the iBook is a wonderfully handy device to have around for the rest of your computing needs too... all the iLife apps and integrated address book are also godsends, with no PC equivilant to match them. The iBook ain't gonna play games very well, but neither is any $1000 PC Laptop. You can play Warcraft III on it if you have enough RAM, which is better than the PC laptop would do at that price, anyhow, most cheap ones have crappy 8mb integrated graphics, and the iBook has radeon 7500.
Anyhow, I think I've made the case... I'm a CS Student at the University of Wisconsin, and I love the OSX Project Builder, and I also like having the option to use eMacs or vi to code with as well. OSX has it all: Unix development power and stability, but it's still not a pain in the ass to use to do your normal multimedia things, and the Hardware has it all together too, it's Extremely durable, connectable, and the battery life is also superb.
