Time to Upgrade?

Hey Vergeins (O_o)

So i bought my 15in macbook pro back in 2008 and have used it EVERY day for hours on hours since then. Being an undergrad is pretty demanding on one's machine and mine is starting to show signs of its age, e.g. running slower, apps taking much longer to open. It has lasted me so long and i know many of my friends have had several PCs whereas my macbook has outlasted their newer machines.

How long have you had your mac? And when do you plan on upgrading?