The thing with swing is: Swing apps doesn't look like native apps regardless on the platform. People don't like this!
I have written a Lotus Sametime client for my company, it's 100% Java with Swing UI. It has nice improvement compared with the original Sametime client form Lotus and it even runs fine on Mac and Linux. But: Lots of Mac users asked about the client, but the dont like it, cause it does not look like a MacOS9/MacOSX application. Same I heared from Windows and Linux users. "Nice features, but the UI sux"
I tried SWT as experiment. SWT seems to be somewhat faster as Swing and I am getting good feedback so far.