it really varies from place to place and company/industry. Which probably means its fading out. I recently went through a few rounds of interviews with several people at a large software company and i did not send thank you emails. I was given the job but it was brought up over beers later on with boss and peers how i did not send thank you emails. they mentioned how during their interview process that most people were not doing that and it seemed to them that was becoming outdated.

Now i was briefly a hiring manager before and i hated getting follow up emails from people i interviewed. It is so obvious that people know it's something they have to do and just kicked out these canned scripted thank you messages. Most people's inboxes are already full and they are busy why would they want this?

And my personal opinion is that, honestly they should be thanking you. I mean, they need help. They put out a "Help Wanted". You have skills that can help them. They asked if you wouldn't mind taking 3 hours out of your work day so you could go down to meet several of their team members so they could evaluate you and help them make certain they are hiring the right person. Maybe they should be thanking you?? It's a two-way street.