I have discussed problems with missing dispose for SPWeb and SPSite objects earlier on my blog (e.g. here and here) and Roger has provided a guidance for specific coding patterns which can cause problems such problems.
In the last couple of month I have been involved in a project driven by Roger Lamb to create and test a tool which allows to identify such incorrect coding in a compiled dll. The outcome of this project is the SPDisposeCheck tool which has now been officially anounced and which should be available in a couple of month.
See here for details:http://blogs.msdn.com/sharepoint/archive/2008/11/12/announcing-spdisposecheck-tool-for-sharepoint-developers.aspx
Any idea when this tool will be out? i recently ran across a client project where it could have REALLY come in handy.
a release date has not been announced yet.
Expect a couple more months.