I've done a few test conversions from SMF 1.1 and I must say I'm pretty impressed with the converter. The thing I like most is that the converter preserves the passwords.
During my test conversions I ran into a few issues. The first few times I ran the converter, it hang when converting the posts. It turned out I had a post on my forum where a member tried to embed a photo using bcc codes. The post ended with /[img[ and the converter didn't like it, but this was easily fixed by editing the post and removing the tag. The next errors I encountered were related to polls. It seemed there were a few duplicate, orphaned polls so I just deleted the ones the converter had problems with. These issues were easy to fix.
Now that I've got everything converted I'm going over the forum to see what's been missed. The only issues that I have discovered so far, are: Signatures were converted, but ended up under 'About Me' in the user's profile and don't show up under posts
Personal Messages were converted but are nowhere to be found (although there was an error which I'll have to look up)
So far so good. If I can get the above two issues sorted, I only have to come up with a strategy for letting the search engines know about the restructured URLs (going from www.mysite.com/forums to forums.mysite.com) and create some smart re-directs. Just a few more weeks... Edit: the passwords don't seem to be preserved after all! Am I missing something?