We're also very happy with it. I have a RAIS array of two servers each with RAID1. So our Postgres database is configured on a quadruple-backup setup thus:
Postgres /var/lib/postgresql /dev/drbd1
primary server --- secondary server
raid 1 raid 1
2 x X25-E SSD 2 x X25-E SSD
The servers are connected back to back by a direct gigabit ethernet link, and we use DRBD in protocol B (memory synchronous).
Thus all transactions are guaranteed to hit the disk, we get fast performance, and excellent reliability.
Cutover from one machine to the other is really easy, and takes 2 minutes. The docs for DRBD are also very good.
There are 2 things to note:
* Write bandwidth this way is about half what it could be with a single server.
* Avoid the risk of "split-brain" at all costs. For us, this means a manual failover process: dataloss is very bad, but a few minutes of downtime is acceptable.