Laptop screens typically look fairly bad when at anything other than their "native" resolution. A bit less flexible than ye olde CRTs in that respect.
Though this is much less the case with high res screens, Apple's retina laptops for example are usabe at different resolutions.
The difference is how the signal is sent. When you change the resolution in XP for instance, a low res picture gets sent to the display which then has to up sample it, and it looks sucky. On the new MBP the picture sent is always the native resolution of the monitor, you just change the size of the UI elements according to your preference.