Just downloaded 6.1 directly from Dymo and it works great!

Two tricks that helped me get past the problems I was having, and others have noted, involving the installation (and the apparent non-installation issues of running the installer but nothing changing):

(1) delete the Preferences plist file before running the installer, and empty the trash; and

(2), uninstall the program using the installer (you'll get the typical "files were in use..." message) and then run the installer.

I can now use 10.3's own Address Book directly from Dymo Label! This is the functionality I was really hoping for in this program. (To do this, simply select "Use Mac Address Book" under "Address Book" in the menu, and be sure "View Address Book" is checked in the same menu. Perfect!)

I'm now back to recommending this device and its software to clients and friends.