FogBugZ 4.0
We've been using FogBugZ since 2.x. We've just upgraded to 4.0.
The new version is quite nice. It looks nice, and has small improvements in a lot of areas that make it more usable, but I was not really suprised by any new feature, until I saw this one [http://www.fogcreek.com/FogBugz/images/50PctScreenshotTool.png]. Basically it's a task bar application that lets you capture a screen shot, crop it, and attach it to an existing or new case. The taskbar application has also a 'New Case' option that takes you directly to the New Case page, which is also very handy.
However, I was not very pleased with their upgrade pricing strategy. Even if Joel wrote some articles about pricing that I enjoyed, their pricing sucks. Basically, each day that passed without us upgrading to the new version, the upgrade was more expensive.
They support is $0.05 per day/user, and the only way to upgrade is to have a valid support contract. This means that if you did not pay support after the standard support ended, you need to pay for it anyway to upgrade. So, we ended up paying around 2 years of support which we did not use.