I’ve had a couple of problems running SWT applications on Mac, in particular, getting balloon tool tips to appear and incorrect invalid thread access errors. It seems that the Mac specific VM option
-XstartOnFirstThread is the cure! It even addresses the bug I reported here!
It seems that by default, Java will not start on the main thread. Cocoa/Carbon starts it all and as a consequence, the SWT UI thread might get associated with it and not your main application thread. Therefore, whenever the application tries to access it (even though it looks like it owns it in your code), it may not and invalid thread access hilarity will ensue.
The flip side to this is that AWT/Swing apps and plugins might have problems.