Thanks for starting this thread as it nearly mirrors the questions I am having. I have always gone for the "tiny" form factor...first a small 12" iBook and next a 13" MacBook. During school, the iBook/MacBook line was sufficient for what I was doing and probably still is for much of what I currently do (word processing, web browsing). However, toss in needing to run Windows, a dSLR camera, Photoshop, etc. and my needs for the pro line are greater. I am not wild about going up in size and the sacrifice of portability to for me so I wonder if I can just make due with the 13". The biggest thorn in my side is that I really would like to have a MBP/iPad team but the cost of the 15" eats up the iPad money....yet the 15" would need the iPad more to meet my portability needs. Thus, the 13" seems the better combo for that reason...and around and around my head goes.
The only big reason I am considering jumping to the 15" is to ensure that I can run Windows smoothly when I need it (sigh). However, save the windows and small harddrive, i am pleased right now on my MacBook 13" (it was purchased when the first black MacBooks became available).
OP: I can move this to another thread if you prefer...it just seems we have the same questions so I hated to fill the forums up with similar threads.