We've done two of the 10 or so shared hosting database servers. There are some kinks we're still working out. Right now we can't seem to disable SHOW DATABASES, which is freaking some people out on the upgraded machines (despite the fact you can't select the other databases and it's totally secure, people have really gone bananas about seeing the names of other databases).
We're sending Level 4 announcements to people on the individual servers as we upgrade them. We expect to have this all done, done, done by the end of next week! This time no fooling!
Oh yeah, and PHP is 4.3.4 everywhere now too!