I have the top spec from January 2010, which I believe is the Intel i5 2.66ghz, 4gb DDR3 RAM, 1TB Hardrive and the graphics card can't remember what it is...512mb I think though.
I want to upgrade because it's either upgrade the whole computer or just upgrade the ram and graphics, also it will be my last year as a student so I wan't to reap my benefits now ;P
Other than this, no reason really, it runs perfectly, and is still fast.
Oh and I want them to fix the mini display to PS3 thing and include the thunderbolt connection but if they do that or not, I don't know...
I will offer you £50 and even offer postage and packaging. Send me your details and I transfer over the money, job done!