It's been mentioned a few times in this thread, so just to touch on it:
Yes, THF and TWF can be a severe detriment and resource drain in the hands of a BAD player. I would caution some of you healers though...in the hands of a GOOD (twitch) player, properly built and equipped for either style, it is outputting at least double the DPS. Stuff dying twice as quickly = 50% incoming damage attempts. And while you'll notice those players taking a little more damage, do try to notice whether ANYONE else is taking damage (THF+Glancing Blows+Cleave, etc. = all aggro on one player).
I took my new lowbie (2 rang/1 rog/1 fight) into an STK Hard group last night. It was a decent group, but no real tanks (2 rangers, a rog, caster and cleric, all 4s). We were all TWF's. The poor rogue sucked and died multiple times when he went off ahead (bad TWF, first melee character). I, however, always led the kill count by 4-5x the nearest rangers and rarely took any damage (except once while I was held at the end of Part 2). Why? Because I know how to play TWF and am built around it. I also know when AC is important (~30 AC is optimal all the way to pre-gianthold). Don't automatically condemn THF/TWF and don't unfairly judge it's effectiveness even when someone might be taking all the damage (spread that damage out to all melees, and your cleric job might actually be harder).