One addendum to Eliot's "both our offices hold open office hours"; we (10gen) also recently opened an office in London.
Although we don't yet have a fixed office hours schedule, we typically hold them every 2 weeks. The exact dates are announced via the local MongoDB Meetup Group°; we always hold the hours at "Look Mum No Hands" on Old Street.
At least one (and often several) of our Engineers make themselves available during this time to answer any questions and assist with MongoDB problems.
Although we don't yet have a fixed office hours schedule, we typically hold them every 2 weeks. The exact dates are announced via the local MongoDB Meetup Group°; we always hold the hours at "Look Mum No Hands" on Old Street.
At least one (and often several) of our Engineers make themselves available during this time to answer any questions and assist with MongoDB problems.
° http://www.meetup.com/London-MongoDB-User-Group