Part of my problem with Steam is the fact that all your games are tied to a single account.
For any online service, there's a nonzero risk of getting your account banned. Usually the ToS gives the provider wide leeway to do this. For example, you might make a controversial forum post, or relieve stress after a bad day by using strong language and calling people names in multiplayer, resulting in a ban.
If you have a different CD key and account for each game, like Blizzard did on the old-school battle.net back when they were cool, then the most you're risking is a single game, and only the battle.net multiplayer feature of that game; you can still do single-player and direct TCP/IP multiplayer.
OTOH with Steam, you're risking your entire collection -- potentially hundreds or thousands of dollars worth of games -- if your account gets banned. And you can't play single player, since a lot of games require Steam to run.
As a result, I only have a couple games on Steam, and don't do multiplayer on Steam. More than once, I'd been ready to purchase a game and changed my mind when I saw it was Steam-only (e.g. Torchlight 2).
