I understand what its like to announce an upgrade, then something doesn't go right and your inbox is full of harsh comments. It is a shame things didn't work out as well as you had planned
The problems you encountered are almost entirely due to the import script and not the actual threads program itself. After my upgrade way back when threads first came out, yeah there were some issues but once the forums were up and running and users had a week ro so to get used to the new look they all loved it along with the features.
I think if you get your users your lost and PMs and stuff back and imported corectly you will find the program is very fast and your users will love it
