Digital stores are good but I prefer multiple stores. I posted a link to Red Faction Guerilla for £3.74 here, and someone posted they weren't interested because it wasn't Steam and they like their games all in one place.
THIS sort of scenario shows why this is a terrible idea.
When it works, Steam is good. But installing/playing your games does rely on active servers or the offline mode working, as well as on your account not randomly being locked out.
The hacked account thing is a big issue too, and Steam should do a lot more to prevent and educate about them.