At JavaOne this past year, there was a session called Extreme GUI Makeover. In it, the panelists took a simple, plain-Jane application (a Swing clone of the Thunderbird email client) and added GUI bells and whistles until it ended up looking fancy-shmancy.
This session not only showed how some GUI punch can really affect perceptions of an app, but also showed just how customizable Swing could be. Sun has recently made the actual presentations available over here, but I’m still patiently waiting for their source code to be released (which they claimed they’d do during the actual presentation).
(I’m reminded of one of Joel Spolsky’s big three pieces of advice: obsess over asthetics).