What kind of a userbase and hardware specs are you running? Did you tune the database or is this a vanilla install (besides the max_connections)?
Our installbase is quite large, with a very busy helpdesk: lots of active agents and incoming e-mails. We were seeing the same sort of lock contending issues and even deadlock situations. We started monitoring and tuning PostgreSQL and now deadlocks and locking issues are significantly less and mostly gone.
Giving advice on tuning parameters is dangerous, as your situation might be completely different compared to ours. We started by logging very slow queries and all lock_waits, which revealed quite a lot of slow queries due to improper database tuning (the next-next-next-finish install). We carefully tuned the database over the course of a few weeks, seeing performance increases and less locking issues appear. We still experience some deadlocks now, but the performance is acceptable at this point. I might be able to give a few hints if I knew more about your config specifics.
