I am a college hire, so my interview process began at a campus job fair. Fairly standard technical questions (basic OO, DB, and algorithm analysis), but no deep personality questions.
A few days later, I received a call inviting me to an on-site interview. They were very accommodating to my schedule, letting me pick any day I wanted within the next couple weeks. Generally companies have set days for interviews, so this was quite unexpected and already set Salesforce above most others.
The on-site interview was a whole day affair. It started at 9am with a 2-1/2 hour programming test. They sit you in a room with a laptop (with internet), give you a problem to work on, and come back a couple hours later and take you to lunch. The programming test emphasizes scalability over completeness. While I am sure finishing the program is a plus, they seemed more interested in the overall design you choose and if you put any thoughts into efficiency and scalability (i.e. what data structures you used). If it's any indication, I didn't finish the program, but still got an offer.
After lunch, there are a series of 1:1 or 2:1 interviews (~4 hours total). Employees from different teams come and talk to you about various topics, such as security, basic network/web knowledge, OO design, .Net knowledge (although this might have been unusual since most development is in Java, and even the .Net stuff is being converted to Java), and DB normalization. It's a bit rough, but the interviewers realize that you probably don't know everything about every topic. They will all have a copy of your resume and they tend to center questions around what is on it. That means you have to be confident with whatever is on your resume and they do expect you to talk in detail about anything on it, but they try not to ask questions on stuff you probably don't know.
Overall, I came into the interviews with hesitation, but left feeling confident and excited about the prospect of getting an offer. The employees seem very excited to be there, and there is a certain electric atmosphere that is apparent when you walk into the office. Everyone is in low-rise cubes, which fosters collaboration, but means less privacy. The views of the bay are fantastic and very relaxing.