Computer "years" are like doggy and kitty years. The life-cycle of consumer electronics is getting shorter and shorter- with cell phones some wireless service providers are making it easier to "upgrade" sooner, presumably due to consumer demand, and not for increasing sales.

With my electronics hobby, I have to fight the urge to purchase the "latest and greatest" devices. I'd love to buy an iPad Air, but my 5 yr. old Macbook is still doin' what it's supposed to do.