I asked the alt.net group what issue/feature tracking software everyone would recommend, and thankfully I got a lot of responses about what people are using or have used in the past.  Really useful stuff.  It would take an individual years to glean this kind of first hand experience.  Here's a summary of recommendations (good and bad):

• TRAC - Python based OSS app. It seemed a lot of people have used this.  Most people think it's OK, but the consensus is that it's kind of "wonky" at times.  The UI isn't particularly pleasant, but Ayende did create a simple Winform UI for it at one point - not sure it still works or how well.
• Mingle - Developed by ThoughWorks.  ROR app.  The UI is pleasant and customizable.  The pricing is different, it seems you pay monthly.  Wave of the future, especially for software that gets released frequently (permanent beta)?  Compared to the competition this appears to be a rather expensive option - but possibly worth it.
• FogBugz - The UI is pretty simple/clean, and has a good dashboard.  I liked the fact that is contained "evidence based tracking" which sounds really smart and useful - as long as everyone enters their actual time on a task accurately.  Phil Hack said, "...FogBugz is hands down awesome. Anyone that disagrees with me, you're wrong. End of story."
• StoryVerse - MonoRail reference project or real OSS based project?  The code AND the UI look really clean.  I'm not sure if this is still active or how full featured it is, but it definitely looks promising.
• Gemini - Got some mixed reviews, but I think most people gave it a +1.  It looks like a lot of companies are using this one.  Integrates great with SVN.  The screenshot of the home page reminded me of Jira.
• Elementool - Fairly cheap.  Free version fields.  From Donn, "Unintuitive and just a hassle to use. Never integrated it with anything though. I wouldn't want to. I just want to STOP using this product."
• Lighthouse - Looks like a hosted ROR app?  From Brian, "It has rough edges in some areas, but overall is a very nice interface, and you can use email to create and comment on issues.  It only has ONE status field (which at first seemed limiting, but then I realized was liberating - at least for this project).  If all you are doing is tracking open items (for example on a maintenance project) it may be all you need."
• TargetProcess - ASP.NET agile management tool.  It will manage bugs, features, and support tickets.  It integrates with SVN.  What's cool is that it uses NHibernate to data access, so it appears you could use any RDMS that NHibernate supports.
• BugTracker.NET - This is a very simple OSS ASP.NET app, but one look at the code you'll run screaming. 
• AxoSoft - TODO: more info
• MS Project Server - It's "enterprisey".