I've just started using it, and the first week seems OK. I use Lotus Notes at work and have found this is a great enhancement to my ability to organize Notes todos according to my modified GTD approach. BB Task Pro blows away Blackberry's Tasks program.
The menu organization makes usage a bit clunky, but manageable. The developer is promising the product will evolve, so I'm hopeful minor inconveniences will be resolved quickly.
I also like BB Task Pro more than NextAction because it allows the flexibility to organize by date - not very 'GTD' of me to want this, but it fits my style of work.