This is something I've thought about for a long time. Do you really want Apple to become like M$ where you spend hours typing in key numbers, keeping up with little scraps of paper and spending time in a hold queue just to prove you didn't steal something? I'm assuming your answer is no. If that is the case, read the EULA and abide by it. The "temptation to steal" is not irresistible. When you study the EULA, you realize that instead of being asked to buy the "Family Pack" for $129 (which also had no DRM), you are only required to pay one time for Lion and you are granted the license to install it on any computer you own "or control". This means the family pack price for Lion is $29. Nice.
Besides, I don't think Lion (or Snow Leopard) are where Apple expects to make a ton of money. I think they are banking on the OS X app store growing up to be more like it's older sibling: the iOS app store. I would think Lion revenue is used mainly to cover the increased support load helping upgraders who run into trouble. I'm pretty sure Apple gets a 30% cut of OS X app store revenue.
Apple just came of yet another record setting quarter. Surely this means that by "trusting us" Apple is doing something right. Based on their current success and excellent rapport with customers, I don't expect Apple to start saddling us with DRM and CD key numbers any time soon.