
Java Swing comes with "pluggable look-and-feel technology", which essentially boils down to the fact that interfaces can be "skinned" (although this is simplifying a tad) and is therefore, extremely flexible. By default, Java ships with a cross-platform look-and-feel (LAF), which means your apps can look consistent across all platforms, or LAFs that mimic the look of a specific platform, say Windows, for example. However, one of the chief complaints of Java desktop applications is its "look". It basically stems from two issues:
having diferent toolkits on the same platform doesn't really bother me as much as ugly looking stuff like (default) swing. Take a look at trillian 3, simply beautiful http://cerulean.ord.cachenetworks.com/img/features_screenshots_3x1....