If you want bang for the buck, I'd go with the i7. That little extra processing power will certainly help, and I believe the mobile i7 has both Turbo Boost and Hyperthreading, which will let it hold its own a little longer.
Assuming you plan to keep this laptop as long as you did the other one, definitely go with the i7. Though I wouldn't be surprised if the MacBook Pro gets a refresh soon. That line is usually updated 3X a year. and the last refresh was mid-2010. We're getting towards Late 2010 now. This is just speculation on my part though.
Ive been a Mac owner for 6 years now. I previously had a Macbook Pro, g3?, it was old (I had it for about 5/6 years, dropped it at least 3 times, crashed on top of it riding my motorcycle, and it fell out of my truck), but I loved it! I am currently looking at the 15", and I cant decide on either the 2.53 i5, 2.66 i7. The money isnt what Im debating on, they both cost a lot, but I want the bang for my buck. So which ever of the two is more worth it is what I want to know, along with a great battery life would be great!THank you for your help!