My wife just got the 17" (to replace her old 15" MBP). She does a lot of document work (she telecommutes), and puts two documents up side by side. I offered to hook up an external monitor so she could use a smaller MBP - but no, she wanted the 17" and she loves it. It's basically a desktop replacement, though. She will move it around the house - but when she leaves the house she takes her 1st generation Air.
My MBP is only 15".... so yes, her computer is bigger than mine. But I've got a Mac Pro at my desk, so I guess that evens it out.
That 17" is nice though. When I've had a chance to get my mitts on it, it's been a really nice experience.
"Now's not the time for **** measuring, Stuart!"
Sorry, couldn't help it.