I don't use anything really. I get my posters from google and the description from a movie rental website and use doug's scripts to input them. I would use metax but everytime I try and tag a movie it just deletes it. I have lost about 5 movies through metax.
There was a bug to do with losing files when the disk filled, which has been fixed. I've also seen one caused by a crash which resulted in a lost file as well.
That said, I've tagged 400 movies with MetaX and lost 2, one of them to a bug that's been fixed.
Cheers, Ed.