I've interviewed a lot of people and interviewed a lot myself. When I'm interviewing people I don't pay very much attention to what they're wearing unless they look just completely ridiculous.
Whenever I go to an interview I wear a suit (and I'm in Silicon Valley and work in tech, although I'm in the management chain now) but not a tie because they're not comfortable for 8 hours of interviews. Out east they are a bit more conservative so I'd say suit and tie.
[brag]I've never not gotten an offer.[/brag]
I do recall when they flew me out to Silicon Valley for my interview at my current place, and the first person to interview me was totally NOT in a suit (flip flops, shorts, t-shirt, tattoos, the whole shebang) it didn't seem to bother him or anyone that I was in a suit.
Finally, do what makes you feel the most comfortable. If you're not comfortable with how you look it'll come through confidence wise. I think one of the reasons I wear a suit is not to impress them but because I feel more confident in one. I know it's silly, but there it is.