The original 13" unibody Macbook was already a fast computer but the new 13" is even faster! I think the 13" MBP would suit you just fine and now that it has a decent screen and fire wire 800 there really are no downsides to a 13". You just need to decide if 13" is enough screen for you. i find that if you don't do much multi tasking 13" does the job but if your like me and like to have itunes, safari, photoshop & a few pages in word open you'll find yourself cluttered with 13". its like working on a small desk you won't have enough space for everything to work efficiently.
now if you're willing to work with 13" you just need to decide whether the 300 dollar gap is worth the extra 2 GB of ram, 90 GB more HD space and slightly faster processor.
also don't forget to look at the original unibody macbook is available from apples refurbished store for only 950 USD is the money saved worth the lack of FW 800, quality screen, backlit keyboard, SD slot built in and last but not least the removable battery life is nowhere near as good new built in style offered on the 13" MBP 7 HOURS!!! (i think thats all the differences but i'm not 100% sure on that)
anyway as for me the 2299 USD MBP 15", 2.8, 500 GB HD, 4 GB ram, 512 dedicated ram is my choice. i think i might run out to my college bookstore tomorrow and pick one up