It really depends on what it is. I was slow to switch from tapes to CDs, but that’s because I was 14 in 1997, and tapes were way cheaper than CDs. Especially if you went to the used music store. They were also easier to put in my backpack than CDs.
My computer? I replace it when I feel it’s too slow, and I get as nice as I can get for the price I’m able to pay. This usually means I’m one level behind the cutting edge, maybe two.
Cell phone? The new Blackberry Bold (the 9700) came out on November 22nd for my cell carrier. That’s the day I got it.
Mp3 player? I took forever to get a new iPod. I had a Wal-Mart brand player for a while, and then my dad gave me his year-old iPod. I finally broke down and got a new Touch about a year ago. I got it about a week after the 2G came out, so it was the newest available at the time.
Car? Heh. My car’s 10 years old, and I’m happy with it.
I guess I go with early adoption on luxuries, and tried and true with things I can’t live without (IE, my computer and car).