Hello!
First of all, congratulations - this is a very nice application, with a lot of potential.
I have some suggestions - some of them could be rather ambitious 
, but anyway, they might give you some ideas:
1. Better integration with Windows Explorer, meaning that tags could be displayed at the "tags" column of Windows Explorer, as well as at the Windows' tags of a file (right click on a file and go properties / details to view them)
2. Exploring the possibility of a connection between the TaggedFrog's tags and the tags of other applications (e.g. Picasa, Firefox etc).
3. Exploring the possibility of a connection between online applications like e.g. delicious and TaggedFrog
4. MS Office and OpenOffice integration. E.g. when I save a document on Word, I could also be prompted to provide tags
5. When you single click on the programs icon, it could display a tag cloud, providing you with direct access to your tags.
6. Tags could be kept at the file's / folder's metadata. That way, if I move a file / folder, it keeps it's tags. Also, if I format my pc and reinstall TaggedFrog, I don't loose my tags.
7. Ability to backup my tags' list and move it to a different computer.
8. Option to synchronize my tags across multiple computers
OK, I think that's enough for my first post 
Keep up the good work!
