I was curious and hacked a mini Netbeans RCP app with one window and exported it as "Zip". The archive contains a launcher "exe" file, my "hello world" plugin/module and the whole RCP infrastructure. The size is 4.08MB. However I deployed all RCP modules - so further optimization is absolutely possible.
This "hello world" application starts the first time in 10 seconds. The next starts are faster than 2 seconds (with splash screen...). I measured the performance on JDK 1.6 and my notebook (Oracle, Glassfish, VMWare with XP, Netbeans 6.0 and some UML tools ran in parallel) on Vista...
The Netbeans RCP based visualVM application takes 20MB on the hard disc (after installation). However this application comes already with subset of the profiler and nice visualization. It is an extendible, opensource profiler which allows the monitoring of local and remove JVMs.
So Netbeans RCP apps seems to be really lightweight :-).