I've used the current 17" MacBook Pro, and the 13" Macbook Air extensively. I have also used the Sony Vaio Notebooks on a regular basis (But have never owned one).

All 3 I listed above are great, I much prefer the 17" MBP over the other 2 I listed but I find them all usable (I am extremely picky about computers). Apples laptop design and construction is really unbeatable in my opinion but they do carry a heavy price tag (but not an unreasonable one. Spec for spec they are competitive)

I triple boot on the 17" MBP (OS X Lion/Windows 7 Professional/Red Hat Enterprise Linux) I use engineering software such as Autodesk Inventor Professional, Solidworks, AutoCAD, MATLAB, MathCAD, LabView, FileMaker Pro Advanced, and a few other less known programs as well. Overall the 17" MBP is an extremely well built machine and is starting to get enough power under the hood that I can actually get work done on it (and not have to use my desktop as much)

I mainly use my GF 13" MacBook Air for media and business apps and is great on the go. very light but is actually a real computer vs Crapbooks (PC Netbooks that are so under powered that can barely run their own OS) I use the iWork, MS Office, Filemaker Pro Advanced, and iLife applications on this computer and it handles them really well nothing like the previous generations of the MBA that were underpowered in my opinion.

The Sony Notebook that a good friend of mine has is a decent machine, not up to the specs that I like but he isn't into the same kind of hardware heavy programs that I am. For its specs it runs well, my biggest issue is the same issue I have with 99% of most PC laptops, they are very poorly designed. the airflow/cooling systems are terrible and can't handle the heat put out by the factory hardware... unacceptable. They also just don't feel solid in your hands (when you pick them up)

It all really just depends on what type of user you are.