Really pleased with this little tool so far - only one thing extra would make it truly ideal for me - auto-syncing from Thunderbird -> Mobile when things change - will that ever happen or is it a limitation if the Activesync API?
Yes you are not the only one to be interested in that feature. It is not a limitation of ActiveSync. It's just that it requires some development to implement it. It will be done. However, I cannot tell you exactly when for the moment.
Well, it's not so much of a problem at the moment anyway as I can set BS to sync every minute and that works fine.
I'd also like to add my voice to those requesting Thunderbird 2.x support I was surprised to find so many extensions are dropping 1.5.x support already ...