Pros
There are many company benifits (paid lunches, "unlimited vacation days", lots of social events, etc). The work at 10gen is interesting thanks to the very interesting technical directions the product has taken (mostly owing to the awesome work done by the CTO and the upper-level engineering management I think). There are a lot of very smart engineering folks!
Cons
The engineering team and the sales / marketing teams might as well be in different companies, which is odd for a company this size. Also, I personally found some members of the sales team a little unfriendly towards the engineering staff. The pay is industry standard, which is OK... However, for a company with large amounts of funding in the bank (which is public knowledge FYI), I find it irksome that the compensation isn't a little more generous.