Dennis holds weekly office hours where anyone at the company can meet up with him and ask questions or voice concerns. In my first month, I met with him a couple times and asked him questions about how he raised capital, his relationships with investors, and his experience with startups. After our first meeting, he let me know that I could grab coffee with him anytime. Foursquare really seems like a small startup despite there being 120 employees.
In response to some questions below about how snippets work, it is not necessary to read the entire company's snippets. It is a Twitter model where you subscribe to people's feeds. I'm following the exec team, my manager and other guys on the web-client team, and a couple of my other friends.
I saw that some comments about wanting to work for Foursquare, and I just thought I'd leave a reminder that we're hiring =) https://foursquare.com/jobs/