I've been using AW2K for just over a year now (just renewed my licence). I was a bit disheartened for a while over the program as it seemed that the developers were letting it slowly die.
Now that they have converted it to the Ebay API, it is soooo much faster and will no longer have the issues of having to be updated everytime Ebay changes a screen layout.
Having tried many many desktop and web-based applications, AW2K is in my opinion one of the most stable and well rounded apps available. Others have commented about the clunky or out of date interface. Once you're used to the interface, you don't even think about it anymore, except when you keep finding more and more features hidden away that you didn't know existed. Even after a year of using it I'm still finding new things and better ways to do old things.
The reason for 4 stars?
Like all apps I've tried, there are quite a few things that could use improving. The auction templating system is woefully out of date and needs an overhaul. The built in email system is antiquated and really needs to be able to accept html/mime emails. The reporting is adequate, but the custom reports aren't all that configurable. BUT you can easily link the paradox database into Access to create any kind of report you want - if so inclined.
Support is outstanding. Thom (who I think may be the only one behind this software) is amazing. He doesn't appear to sleep and answers support questions often in minutes. And unlike some of the other companies who shall remain nameless, he actually has an answer to the problem rather then blaming it on the user.
Since everyone's Ebay business runs differently, this software isn't for everyone. But it's the best I have found and for all of it's shortcomings, the feature list and price far outweighs any issues imho.