Despite it's issues (and I can't say that 683 is that many considering the nature of the application) Tomcat is the best Open Source Servlet engine you can find. It is generally regarded as being standards compliant and works for every application I have ever written.
I must agree with CD on this. Tomcat is good open source code. If you wan to discuss buggy code take a look at some of Microsoft's offerings.
I can't think of any major software (or minor come to think of it) which has zero bugs...