I've been playing with Error Prone by integrating it into the build process and to see what kind of warnings it would produce. So far I'm positively impressed by the coverage and usefulness of some of the implemented checks. See attachments for results.
Unfortunately there are still some issues on how the analyzer is effecting generated code and used guava versions, see #492. In case those issues have been solved and the resulting code isn't affected by the analyzer, I'd suggest to add it to trunk with warn only behaviour and some less useful checks disabled. Alternatively a new ant target could be added, maybe with build breaking checks and CI integration.