My two shekels' worth on the topic -
It would be very nice if we do move that we could keep with YABB - it is used on quite a few other sites that I visit and it generally works quite well - most people can handle what administrivia needs to be done without investing in a bunch of training classes, etc. so it keeps overhead/maintenance levels down for people with other jobs to do.
IT has its database drawbacks too, but I think it is a good compromise. We've accumulated alot of good technical info, so if we couldn't migrate that data it would be a shame.
If you need some donations to help out with the costs of maintaining the site put a sticky up and I think that many will contribute according to their ability. I could certainly
spot you a few Jacksons...