The replication is reliable, it's just that with the 8.0 releases, it's an add-on and not obvious to setup (e.g with Slony have to do special procedures to properly replicate DDL changes, it required having triggers on replicated tables, etc). In 9.0 replication is built in, transparent, and trivial to setup.
Sorry, but pre-9.0, Postgres replication is neither reliable nor easy to setup/admin. It's absolutely the worst thing about (pre-9.0) Postgres, and I'm glad the core team finally caved and made it a first-class feature.
Slony caused us no end of problems (large postgres installations at Last.fm). It's a monumental pain in the ass, it will choke on something, probably when you're trying to make a DDL change, sometimes just at random. Docs/help on trying to figure out what went wrong and how to fix the replication are not easy to find. After you managed to 'fix' it, you will be unsure if the slave is truly in sync. The only way to be confident is to nuke the slave and start over to ensure you have a consistent replica.
That said, I'd still gladly suffer the trials and tribulations of crappy trigger based replication than use MySQL.
I'm looking forward to trying replication in 9.0, it sounds fantastic.
You are correct about Slony but if you do not care about doing any reads at the slave in pre-9.0 you had log shipping and warm standby. Warm standby is perfect for using the slave for failover in case the master crashes or the HDDs break.
Warm standby is very reliable and easy to admin. The setup is not that easy but not too hard either.
