Let me start this with: I'm not a lawyer. There's a chance I'm wrong about this, but I doubt it. You can't sell, rent, or give someone else the games or the extra content from them. Psting your avatar in an online forum where someone else has (obviously) the ability to see it is isn't selling or renting. Don't make a page somewhere where you say "Here are all the awesome GOG.com avatars. Download any of them you like and use them yourself!" That would be not cool. This is a bit of a grey area. Technically, no you probably can't. Your game license is limited to you. But there's some wiggle room. For example, if you bought NWN from us and gave your buddy a copy so that you guys could play multiplayer together, that's not particularly cool. If you played Riven yourself, finished it, and your sister asks "Can I play?" and you give her a copy to play with (and don't play it yourself at the same time), that's cool. In this case you're good, unless you make your buddy pay you to play the game on your computer. If you're just letting him play on your PC while he's hanging out at your house and bored out of his skull, that's fine.

Basically, think of your copy like an actual physical disk. If you lend a buddy your disk (no money is exchanged), you can't play the game while he has your disk. Once he gives it back, you can play again. The one difference between the disk and the download is that you can't eventually sell the download to someone else like you can the disk.

Or, you buddy can be like my friend Josh and take your disk of Freedom Force and never return it. In which case I think the EULA says that you're supposed to go to his house one day and rig a foghorn to go off under his bed at 3.00 in the morning. At least, that's what I did. ;)

Hope that cleared things up.