We tried upgrading to 0.8.4, and while it was somewhat painless to upgrade, we were disappointed to see that compile times for our main app went up by 30%, from 22secs to 29secs, and that a basic non-scientific test ab -n 100 -c 5 http:/localhost:8080/ shows that our app is now only able to server 1.08 reqs/sec, down from 1.59 with 0.7.33.
Note that our app uses vibe for much more than just serving the request. There are plenty of database and client HTTP request traffic.
We are going to stick to 0.7.3 for the time being :(