Some tips from my experience migrating from a MacBook Pro (Penryn 2.4) to the new "unibody" MBP 15-inch. When migrating your data from one Mac to another there are three methods.
Migration Assistant Apple's Migration Assistant software (pictured) is by far the easiest method to migrate to a new Mac and should be used whenever possible. It's the little wizard the pops up at first boot and after installing a new version of the Mac OS. It's convenient and usually the best way to go. I wrote about Migration Assistant in MacBook Migration Strategies.
Nuke and Pave Code for wiping a hard drive, installing Mac OS X and then installing all your applications fresh. This method is the cleanest and best, but it also takes the most time. If you're having major software trouble or carrying a bunch of legacy code from machine to machine, this may be your best option. Rob Parker details a good clean install strategy on his blog that I recommend following. Personally, I'm going to wait until Snow Leopard to do my next N+P
Hard Drive Transfer When I get a new MacBook I typically prefer to physically move my HDD from the older to the newer model. A physical hard drive migration is arguably the easiest method (29 screws notwithstanding) to get your data onto a new machine, however there's one caveat and it's a doozy.
Even though your new Mac may look like it's running the same version of OS X as your old one, Apple ships a custom version of OS X that is designed specifically for the new hardware. Simply dropping the HDD from your previous MBP into the new model probably won't work – at least not well. In this case you should run an Archive and Install from the new Mac's install DVD by clicking on "options" on the first screen of the installer. This installs a completely new version of OS X, then puts back your preferences.