It made me feel like I didn't know anything and was very embarassing. It also changed my outlook on Google, and I'll never interview with them again.
Maybe some tech media company will do hidden camera interviews and publish a scathing rebuke of the practice.
You can always tell the recruiter/coordinator. It's just tricky because you don't want to burn bridges, doing it before you hear back could be read as you asking for a do-over, doing it after could come across as bitter.
If you have a good or bad experience, PLEASE consider telling the recruiter know.
The last place I did interviews at, we'd bring all interviewers into a quick debrief meeting and talk about whether to give the candidate an offer (going off the notes we took during the sessions). It was pretty obvious if someone had a particularly bad session and could be weighted against other peoples' input
Unfortunately it can be really hit and miss