I think it’s all over the place and pretty much depends on the company and kind of position you are applying for. I never know how to truly prepare either. I have interviewed with companies that make you solve quizzes and weird little algorithmic games that have nothing to do with the job you’re applying for, others that rely heavily on the whiteboard and ask you technical questions that really seem to be testing how good you are to memorize stuff rather than your programming skills. I’ve also interviewed with companies where they give you a coding assignment of some kind, and then a personal interview with the people you would be working with.
I recently interviewed for a position where they gave me the coding assignment, a pair programming exercise and then another coding exercise, plus one on one personal interviews. It was a long process but the coding challenges were completely related to what I would be doing on a day to day basis, so it all felt like it made a lot of sense… and I got the job.