I've used Macs ever since I started CS... had an iBook first and then replaced it with my current Macbook Pro about 3 years ago. The most important things I've found are weight and battery life, coding isn't hugely resource-intensive at undergrad level (apart from the odd huge group project or your final year project). For the next laptop I get, I'd like to go smaller than 15" (I find 12"-13" perfect because I've got small girly hands which suit a small keyboard) and preferably under 5lbs in weight. I'd also like something with a longer battery life than my MBP - even when it was new the battery life wasn't as good as I'd like, and at this stage it's down to about 20-30 minutes because I'm still on the original battery.