I've interviewed and been interviewed countless times in the last decade and maybe once I've worn a full blown suit. I don't have a problem with them, but I don't want to look like an asshole when everyone else is running around in hoodies and jeans.

I usually just step it up a notch from whatever the regular office attire is there (either by asking my point of contact or having known the office). If it's full SV/hobo style I'll do a polo and nice jeans. Business casual and I'll wear a nicer shirt and some khakis. If I really have no clue I'll go slacks and a dress shirt.

In my own office (we're all remote) I still wear jeans and a polo most days. Usually just out of sheer laziness.

I'd say it's actually a detriment to wear one to an interview in the Valley. I learned that first-hand (but still got the offer).

The only suit I've ever bought was for a funeral - and I question the logic in that (a rant for another day). Ive had about a dozen interviews over the years from small to very well known companies and I've always just put on jeans and a t-shirt, sometimes a jumper if cold. The only time I did not get a job offer was for a large travel firm in deeside, north wales. They interviewer asked why I thought it was appropriate to turn up to the interview in a t-shirt, my answer was kind of long and opinionated, as the two numpties sat there suited and booted talking about how awesome their company was. Needless to say that was one job I didnt get an offer for, however given that the interviewers were asking questions they didn't understand (e.g. how strings are managed in the CLR) I didn't lose any sleep. I later found out from others it was a shit place to work anyway.

I once interviewed for a job with a "hands on" recruiter clueless about tech culture who insisted I suit up. I overdressed and was interviewed by a VP of engineering who wore ragged cutoff shorts.