First of all: Great product.

You can even use NetNewsWire to save you loads of money for VT Pro:
- Subscribe to the VersionTracker RSS feed
- Create a smart folder, which contains all the software you want to keep up to date

e.g. Match "any" of the following conditions:
Title starts with NetNewsWire
Title starts with Firefox -
Description contains for OS X 10.4 (Brings up new Apple security updates)
Description contains on OS X 10.4 (ditto)
...

One bad thing, though: If your filter rules extend your screen, no scroll bar will appear (Developers, please fix it!!!)