I have just made the same switch, from a mid 07 macbook to a new i5 mbp. I reckon after selling my old one, student discount, and selling the almost free ipod it will have cos t just short of £1k to upgrade with 3 years applecare.
Worth it though, it is unbelievable how much faster it is, especially when on paper it didn't look a lot different to the average shopper. Screen is bigger, and much nicer to use being backlit, 3 and 4 finger touchpad is good too.
Keyboard is a bit shitty tbh, the backlit thing is tacky as you can see the light under the keys which ruins it a bit. I usually have it turned off.