CW jones has some good points, i have a 13" macbook beside that i ran for 4 years and i got my 15" yesterday and it feels massive!!!!! in comparison but when i set my old macbook on top of the new macbook pro, it is 1 inch wider and 2 inches longer, so its very very little i think it weighs 1 more pound, and it runs ALOT quieter having the 2 fans vs 1. And also note that my 15" feels bigger then my brothers brand new 17" HP laptop, its funny how that works >_<, and the gt 330 m with 512 MB of vram means you really wont need to upgrade as soon as you would with the 13". And i have already noticed after having 1 GB more ram then i have ever in my life has i am left with like 500 MB while i am running star craft 2 alone, and with the 2 fans it runs at very very respectable levels, and i don't think i have yet surpassed 30% of my processor used yet so i will have to do my best to max that baby out =D
summary - i bought my 15" mbp fully loaded without the ram or ssd, with student discount and sold the free ipod to help with cost, and i am LOVING this it is an absolutely amazing machine.
p.s. i took a photo of them on top of each other i can post if you would like to see the size difference.