Dell laptop quality has never been good, I can't see that changing anytime soon. I have an IBM T41 and has been rock solid. I have seen various people have various problems with the vaio's as well. One friend went through 4 units on his warranty (he didnt abuse them).
As far as I'm concerned anything over 14"-15' beats the purpose of having a laptop, the portability goes down significantly past that. The IBMs are a good size in every dimension: just big enough to be quite comfortable, still small enough to easily take them whereever you go.
I'v used the 12" Powerbook before and thought it was outstanding. It's not that heavy and the quality is outstanding. I was gonna get one in Sep, but am holding out till they come with the new Intel processors.