- The trackpad. You won't be able to use gestures and multi-touch features. Especially if you use some software that lets you add custom multi-touch gestures, it's really nice to have a huge trackpad with gestures.
- Battery life (and longevity) will almost certainly be significantly better on a MacBook Pro.
- Apple's support is pretty great. If you have any hardware issues Apple will take good care of you. Sometimes you have to push for it, but I've had a 2 year old computer replaced with a new one because they couldn't fix a relatively minor WiFi issue.
- The MacBook Pro displays are really good and viewing angles are much better than most PC displays I've seen. You can optionally bump up the resolution of the 15" MBP to 1680x1050 for $100.
- Backlit keyboard — I thought I wouldn't really care about it, I type in Dvorak anyway so I don't need to see my QWERTY keyboard, but this is actually really nice in low-light situations.
- I've also read that there's a lot more that makes Mac hardware fast than just the tech specs. The hardware is well tuned.
A lot of these are little things, but they add up and make for a really good experience.