For some time now, I have been encountering rather poor performance with STS. Often when I save a source file, STS would spend a long time building the project. CPU usage remained elevated long after control returns to the editor. This is STS 3.1 linked to Eclipse 3.8 platform, so we can't blame e4 here. Attached is a JProfiler-captured CPU profile of one such occurrence. I limited the call tree to the busy thread (non-waiting). Just point your browser at Call_Tree_3.html. I'll be happy to attach the actual session snapshot if you have JProfiler.