Since sneak attack is now able to work on almost every creature (making a powerful ability even more powerful), it seems that limiting it to the first successful attack per round should at least be considered. (Some sort of playtesting is probably needed here.)
Though if it's limited to one per round, maybe get rid of the restriction that says you can't sneak attack a creature with concealment. I've seen that restriction screw rogues out of sneak attacks even more often than does the 'immune to crits' restriction. (Besides, why shouldn't a rogue lurking in shadowy illumination be able to sneak attack someone else walking in shadowy illumination?)
