We were looking for a tracking system for use between developers, support, and sales, and this has been a great match so far. It's easy to use, and the ability to submit tickets by email virtually removes all excuses anyone can come up with for not using it :)
They have been great with support, response time has been great, and a great thanks for importing our bugs from Mantis with a csv export on our end.
The search functionality is also great, with the ability to save and share searches, also the ability to export the search results is an amazing feature.
We highly recommend it!