I've used Personal Brain since the start. While I understand the need to try and get more revenue, it's disappointed to see that if I want to have key features (i.e. attaching files) that I have in v.3, I'm now forced into a relatively large upgrade fee.
So, if I want to keep my existing features and ensure that I'll have support on future platforms, I have to cough up more cash. Wouldn't it have been better to provide existing users who bought a licence an upgrade to Core, so they could at least keep using the tool in the way they have been.
I really don't want to get locked into a continuous forced upgrade path (that was one of the things I liked about The Brain - not constant payments). Sure, Pro has new features - and that should be extra.
Of course, Personal Brain is not the only tool where this happens, but it's causes you to think whether you can live without it - as it's now another thing to find money for.