When I signed up with Good Old Games, I only intended to purchase the Fallout games. I had just started receiving Paypal money courtesy of Text Link Ads and I didn't quite know where to spend it; and here were some games I never managed to catch the first time around, and they took Paypal payments. And the games were really cheap.
Now, close to a year later, I'm surprised I've actually gotten so many. Yes, it's a combination of impulse buys and nostalgia, but on the whole I really like the service. What's more, several (though not all) of the games also run on Linux under Wine, and that means I hardly ever have to dual-boot. (Come to think of it, the last time I booted into my Windows partition was over two months ago.)
By the way, it's GOG's first anniversary this week, and they have a 50% sale on Interplay games: lots of old favorites like Fallout, Descent, Earthworm Jim, and more. If this strikes your fancy, head on over there and tell them I sent you.