Are you doing separate demo/full version, or unlockable demo?
We do separate demo and full version through BMT. My only suggestion when doing it this way is to use the "Never Expires" password option. This will allow players to download the latest version using their original purchase receipt. (BMT has some anti-piracy measures in place so if a customer posted the download link publicly the link link would be invalidated after too many downloads)
As far as notifying customers of updates - we just post it in our forums for the more hardcore players who would be interested in that.