Hey there. Not really an issue that MT has caused because it works pretty darn awesome all the time.
I just helped a friend upgrade from v3.2 to v4.12 and it went well (i was very impressed - ok, less of the ass kissing) and the entries, db etc and even templates seemed to import ok but with a few bugs. Which i'll get to.
The problem i have right now is that when i save an entry although it does save i get an error 500 message. I've checked the permissions on the files and they are 755 on the cgi files. When i delete the message and publish just the indexes again, it works but shows me the error 500 message.