We've been testing it on development machines but we've been running the old ljprotocol.pl on the main site out of paranoia.
Today we made the switch and we're now running the new code. If you find anything that's not working in the clients (or website doing things the clients can do), please report it to support. Don't report 'checkfriends' clients not working... we had just disabled that the other day. It's back on in the new code, though.
Things most likely to break are editing friends, friend groups, history, posting, etc. Anything that a client could do. (The website uses the client's interface to do stuff, so the same breakage would occur in either place usually)
 After checking the known issues box, of course. :-)
 Note that the latest Windows client has a bug where it can corrupt your friend groups if you switch bertween tabs before it's done loading... don't report that. That's a client bug.