When there's a game I'd like to run and can't run at 60+ fps an upgrade is needed. If something breaks then I obviously get a new component.
i've had this laptop for around 2 years at this point, and I don't think i plan on getting anything new until i get more money/this dies. it still gets 60fps on tf2 for like 90% of the time so i don't think i even need one.
I built my first computer a little over 4 years ago, and it still works great and is sufficient to run most games, so I gave it to my brothers. I built a new computer 8 months ago mostly because I had extra money and wanted prettier graphics on some games. I'll probably keep this one for another 2-3 years.
i built my first one feb 2010 and gave it to my dad in feb 2012 after i built this one
I think I get a new processor about every 3 years, and a new video card every year or so. Mostly that's because I've had reasons to build several lower power systems so I take an existing video card for that purpose and then get a 200 dollar card for the gaming pc.