Yar. I tend to download pirated copies when I've lost/damaged my CD/DVD and just want to play it for a bit.
But I know some people who are of the mindset of "well I pre-ordered GTA2 back in the day, didn't live up to the hype/my expectations and now I feel like they owe me forever" - which is saddening and tends to dent the industry a bit. Future developers tend to think "I'll make it a masterpiece, but it'll be cracked and on to download for nothing in a day" and then go overkill with the copy-protection.
If I like a game, I'll buy it - it's giving back to the guys that spent those long nights coding away for my entertainment. It's an incentive to do better, develop sequels, and so on. It's like having braggers rights to own a quality piece of scripting, coding, and a good game. Plus if the company is a small-ish one, then it's a boost to them.