Maybe depends on where you're from. In California it doesn't fly, but you're still expected to not have just a tee shirt and jeans. However on east coast it is still expected most places. Doesn't need to be a great suit though.
The whole point really is that it needs to look like you care about getting the job. If they're looking at many candidates they're probably going to pass on the person who acts as if the interview is a waste of time, and they're definitely going to pass on the person who thinks he is so awesome that conventions can be thrown out.
I don't wear a suit, I don't wear a tie. I haven't worn a suit to the last few interviews. I am not a pro-suit person. I am a slacker. I will wear a suit to a wedding or funeral of course. However I have great difficulty understanding the mind set that wearing a suit would be throwing away dignity. Is this some sort of British style worry that you will be a class traitor if you put on a suit? What's the big deal? No one will laugh at you, no one will think less of you (no one that matters anyway), no one will mistake you for a tool.