I don't play 4e, so can't comment on that game. But with 3.x, we've houseruled away the ability of the thief to backstab during combat. He gets one, and he has to be moving silent/hiding and get surprise to get it. And it can't be in the middle of combat. After that he gets his low HP ass out of there, and maybe plays sniper from a distance.
As for those who say it makes him a useless class if he can't fight--it doesn't the way we play it. We don't have a 15 minute adventuring day. The day lasts until we are all out of hp, spells, and charged items. And I mean totally depleted. Or until the mission is completed. Whichever comes first. That prevents the wizard from stocking up on thief-clone spells because his other spells are needed so much that he would be stupid to try and mimic a thief through spells.
Plus our games are not built around combat. We may go 3 sessions without a sword being swung. A lot of RP and other stuff takes our time. Even when we do adventures, they aren't all fighting. We get xp for stuff other than fighting. Completing the mission isn't always killing the big bad guy at the end.
The thief is still a valuable class in our game. We don't even call him a rogue.