A friend of mine bought an iMac in 2008 and is still using it, mostly for writing, web browsing, and email.
In the 9 years he's had it, he's used up about 80gb of the total storage space.
I suggested that when it's time for a new iMac (his is actually still doing very well, because I've "held him back" to Mountain Lion), he get one with the 256gb SSD ($100 more).
I think he'll do just fine with that for the -next- 9 years!