I game exclusively off a laptop. Depending on what you're upgrading, it's not that big of a hassle. I get the back cover off and right there is the ram and harddrives, the two most commonly upgraded things. Do a bit more pulling off and you can get to the processor.
Recently tossed in a second 500 GB harddrive. Cost me right at $80. With it having 6 gigs, I don't have much reason to upgrade the RAM.