My interviews with NVIDIA went pretty well, although I didn't get the offer. Here is the rough process I went through:

1. Submitted my resume at the Siggraph job fair in August 2009.
2. Three weeks later, I got an email from the recruiter for an initial phone screening.
3. One week later, I was interviewed by a software operations manager. He asked about my expertise and told me he would forward my resume to the dev tech team.
4. After about a month (I thought I was already rejected), I got another email from the recruiter for a 45-minute interview with the hiring manager. All questions were technical, and I answered okay; for some, I only came up with reasonable but not best solutions.
5. I got an on-site invitation the next day and scheduled it for two weeks later.
6. I was interviewed by 8 dev tech engineers. They were mostly PhD researchers and developers and asked technical questions related to their own backgrounds. For about 3 of them, I didn't do well, partly because of background mismatches.
7. I received the rejection one week later.

All in all, I was happy with the experience. NVIDIA engineers are smart and nice.

Some cache problem:

About which part of memory should be cached when you solve a linear system so that the speed-up benefit from the cache could actually be taken advantage of.