Pros
The innovation that this place delivers can't be matched anywhere in the world right now. We're rapidly creating a new industry, with new problems and opportunities, partnerships, and customers. That creates a level of dynamism that you won't see in existing product spaces (e.g. social networking, enterprise software, etc.). Think of this, VMware is building a new OS....and people are using it. Linux, Apple and others have tried but haven't gotten nearly as far. Combine that with some excellent benefits (401K match was great until it was suspended) and ESPP and it's generally worth the effort to stick around. If making cool, new technology that people will pay for is your thing, there's no place I'd rather be.
Kontras
Its a startup with all the problems of a company that grew up too fast. I've seen this story before (as we all have lived through it, I'm sure). It gets big, communication breaks down between groups, there's no formal process for say product planning or structured sharing between big teams (like engineering and product management). Of course we have wikis but we also have sharepoint and a host of other mechanisms. And as you grow big 2 things happen: - you attract less than spectacular talent (people are mediocre otherwise there wouldn't be an average) - the smart people get annoyed when stupid people or anyone the don't know, gets in their way == Politics! You expect it and when you're small you can handle it because everyone is focused on their goal. When you get big, everyone wants to go home on time and stop working insane hours, especially when you have less and less personal vest that makes up a significant part of the company (my options will not be affected by my work, likely it will be affected by the most mediocre person's work).