I’ve got the 17″ and I love it. Yes, it’s a bit bulkier than the 15″, but it’s not the end of the world. I’ve traveled with it extensively the last 6 months and I wouldn’t trade it for a smaller one.
I highly recommend maxing out the RAM; I’ve got 4Gb (third party), and I’ve no performance issues. Also running eSata to G-Drive Qs, and life is good!
Paul