How much better is a free trial for making that harder sale? If I know that any work I put into switching to your thing might get destroyed after thirty days, I'm less likely to bother at all. Whereas if it's a partially-free-forever thing like Dropbox, I don't have to commit as much to either the new way or old way. If I hate it, I don't have to rush to get out before the trial ends, I can just wait until I can't take it anymore.

Partly it depends whether I actually need the "full version" just to evaluate, or if I can get by on the free version, for now at least. Didn't you have a similar issue with BCC, where people would get all they needed from the free trial? I don't remember how you resolved that.