For me:
It works great. Offline messages are working! (retrieval and sending of course). You cannot add anyone though, so friend add/removal should be handled from within the normal steam client.
I don't have any issues with disconnects. I mean, steam itself is not a very stable "chat" protocol so it does go off from time to time, but no biggie. Tuesday (periodical maintenance for valve) is a notable example.
You can get it from the client as well as from the page - make sure to get the development version (and you will need dev version of miranda for it too). You need to scroll down past the icon packs to see plugins, it's there.
I can recommend it; as long as you can live with having to add people via the normal client.
For miranda steam db corruption, I don't know. I had an issue once and the "fix" was to never run the "aggressive" search; only mark all messages as read. Been using steam for months now without any major issues though so...
tl;dr:
What works:Message sending/receiving
Offline message sending/receiving
Userpage visibility
View of the game+server the user is currently playing (if any)
Steam guard login
What sorta worksStatus changing (status message is not present and state doesn't change instantly, a limitation of steam protocol for web api I think?)
What does not workChanging avatar (has to be done from steam client)
Adding a user (has to be done from steam client as well)