I like Jira. We use it to track pre-release software defects and it is quick to do commonly used functions like searching, screenshots, commenting on issues (no, it doesn't integrate with our CVS but we don't need it to). Once the software is released, per protocol, an issue with the software has to be tracked through our Siebel CRM solution (ugh, ugh). Jira compared to Siebel in terms of developer friendliness/usability - no contest.