JAYHAWKBABE  A solution for keychain issue I mentioned below:

After several emails with the developer, it became clear that the issue was with my keychain permissions. I tried to run Keychain First Aid from the Keychain Access program and was told that my keychain did not have the right permissions. On a hunch, I fired up the terminal and checked the permissions on the file ~/Library/Keychains/login.keychain. The owner was set to root rather than my user name. This was easy to fix using chown. After that, Garage Sale worked just fine!

I am still not sure how the permissions were changed. Perhaps the 10.5.4 update I installed yesterday?  (Version 5.0.2)

JAYHAWKBABE  Beware before updating from version 5.0.1 to 5.0.2. The latest version seems to have massively broken access to the OS X Keychain, which removes any authorized accounts and prevents them from being added back. It also produces multiple requests to access the Keychain every time the program is started. I tried redownloading and installing the program and reset all of my old preferences--nothing helps.

I just emailed the developer last night, but need to get my hands on version 5.0.1 ASAP because I have auctions running and some finished ones I need to have. The last backup of the program I have is version 5.0.0 which was recently broken by an Ebay API change. The developer on has very old versions for download (3.5.something) from the website and not recent ones!

Very frustrating! I guess I'll be hesitant to update without backing up the program in the future!  (Version 5.0.2)

BLOOBIE  Is this going to be another notoriously forced upgrade like 4.x was?  (Version 5.0b2)

VIOLISA  I think version 4.1 is a vast improvement. The program's design is sleeker, and the tools are more intuitive. I really like the "cover flow" option where you can browser through templates in preview mode. Another big advantage is the way you can choose photos directly from your iPhoto library. This alone saves several minutes of time per auction. More of Ebay's specialty options are supported, and the the text in the description is automatically converted to html. You can even view user messages about your auctions and reply to them within the program!

My only caveat is that the version 4.1 has been a bit buggy. Sometimes the preview option will make the program unexpectedly quit. But, I've found restarting my computer clears this up and then the program works fine again, without any data loss. I've also had a little trouble with the font size on the uploaded auction appearing larger than the way it was shown when I was creating the template. But, that's easily remedied by simply tweaking the font size to be smaller on the template and using the "revise running auctions" option on the Template menu. You can even make changes on a batch of templates, then select them all and upload all the changes at once!

Overall, I think this program is totally worth it for anyone who's got a lot of auctions to manage, and is computer saavy enough to find easy workarounds for minor issues like I described above. I like the program so much, I'm going to upgrade to version 5 today.  (Version 5.0b2)