I just did an 8.0.5 -> 8.1.6 upgrade with export/import. It takes a while as TerryD mentioned, but you can at least accomplish the bulk of it while the other database is running if you can't afford the downtime. Of course doing it that way requires more work/understanding than just taking the database down to others, exporting a full consistent database, and importing into a new one.

I didn't use the migration utility because of sysadmin issues but I've heard it's also very nice to use.