All of the dev and GWT stuff LGTM. I don't really understand all the nuances of the logging plumbing, though. You might want a second pair of eyes, unless you're really confident in that part.
Questions: 1) Why do you need to prefix the logger name at all? If we've got our own LogManager in DevMode, it can be its own isolated world right? It's very muddy to me to what extent this implementation creates an isolated logger world per client vs. tries to integrate with the JRE. The former option seems cleaner and wouldn't seem to require the unique thread id stuff. 2) Are you subclassing LogManager on the back side to remove the aforementioned prefix? Seems like you'd want to, otherwise Logger.getName() doesn't return the right value relative to user expectation. 3) Are there GWTTestCases for Logging that need update? http://gwt-code-reviews.appspot.com/725801/show -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
