Pros
Salesforce.com is a dynamic environment with some very smart people -- when I first joined I termed it the all-star team. It's no joke. The product at Salesforce is really good -- sometimes it sells itself -- and it's very well thought through and architected. I've worked at a number of other software companies and I've never seen anything like it. Career advancement opportunities are everywhere. Although it's a fairly big company now, it's definitely possible to identify opportunities and take them, even from the very bottom rung of the latter, and management actively encourages it. The executives are also top-notch and generally very accessible. These are the people I want to learn from. They know what they're doing.
Cons
The hours are definitely long, no doubt about that. There are never enough people on board to do all the work necessary. There's always a certain amount of chaos. Salesforce definitely exhibits some qualities usually reserved for startups in that regard -- every day is challenging, but it sure makes going to work fun.