Qt Jambi vs SWT for cross-platform GUI development

Question

I'm currently involved in a project developing applications primarily for Linux (Fedora 10). However, it might be the case later on that we will have to port these applications to Mac OS X and Windows and we don't want to be caught out by choosing the wrong GUI toolkit.*

For a variety of legacy reasons we are locked into using Java. We are in the process of deciding between using Qt Jambi and SWT for the GUI. I haven't much experience in using either of them so I'm doing some small prototypes to try and get a feel for them. So far (just developing on Linux) there isn't much difference between them. However, there's a limit to the depth I can go in a short time. This is why I'm asking for help.

The particular features of interest to us are:

• Frameless windows

• custom shaped windows (i.e. not rectangular)

• aesthetically pleasing

Does anyone have any experiences and/or insights into these two libraries that might trip us up later?

• Agile programming people will no doubt jump on the phrase "might be ... later on" and say we shouldn't worry about it. However, in the absence of other deciding factors between the toolkits, future extensibility options will do. I promise not to write any cross-platform specific code until I have to :)

Update 11 Feb: Thanks for the great answers. For those that are curious, we will probably go with Jambi. It was mostly the style sheet functionality that won me over as they make easy a lot of the custom widget shape stuff we need to do. The Qt suite of examples showed that frameless, custom-shaped windows do indeed work on different platforms, so we shouldn't be caught short down the track. The LGPL release was why we were considering Jambi at all :)