Lol! It's now August 2008 and I had the same frustration as megloman. Why in the name of all that's holy the email couldn't be edited to state something like:
"Now that you have purchased the full version of the application, uninstall the trial version (if you have it installed) and re-install the application from the link provided"
*that* would have saved me a major pain in my butt! If you try to simply install from the newly downloaded file, the app. stays in trial mode. Unfortunately I wasted my twenty bucks anyway because I was using the app. to try to help my issues with Nvidia's badly written vid card drivers, ah well, we live and learn I suppose...
My personal opinion is that one shouldn't write software installations which are counter-intuitive to a user's expectations. Those expectations come from the vast majority of install, upgrade, registration and licensing procedures already available. You end up leaving customers with a bad taste in their mouth about your product.