A lot of these new tech companies are saying that you do not need a suit to do business. For example Google: Ten things Google has found to be true-> 9. You can be serious without a suit.

They probably mean that you can work in casual clothes, possibly on the job interview too?

The job interview is extremely important and you should neglect the first impression that clothing gives. I think you should dress up, more than what you would normally wear when you are working there.

Clean yourself: Brush your teeth, trim your nails, shave and shower.
Avoid: strong perfume or cologne, the interviewer may dislike your choice, no odor is best. Avoid bright, flashy colors and patterns on your clothes, dark blue or grey clothes are best. Don’t wear a lot of jewelry.

For men:
Consider cutting your hair if you have long hair; wear it in a pony tail if you absolutely have to have long hair. No beard, shave that mustaches. If you wear ear rings - remove them.
A business suit is best, white shirt, use a tie (How to Tie the Windsor Knot), use a tie bar, dark socks, and go for a black belt, polished shoes. Don’t have stuff buldging in your pockets.

For women
Make it look professionally, no flashy colors, small ear rings, not too much makeup. Consider having a briefcase or portfolio rather than a purse to have your papers in.