When designing a Swing UI under Matisse, there doesn't seem to be any way (that I've seen) to toggle 
between different look-and-feels at runtime.  It appears that it is only possible to design a UI using the 
L&F that is in use by the NetBeans IDE.  For example on Windows, NB uses the WinXP L&F, so when you 
design a form with Matisse you will see the WinXP L&F.  Likewise, on Mac OS X, NB uses the Aqua L&F, 
so you see Aqua.  But on Solaris and Linux, NB uses the Java (Ocean) L&F by default, so by extension 
Matisse will show the form using the Ocean L&F.

Obviously Matisse was designed so that you can develop a UI and have it look great no matter which 
L&F is used.  But it would be nice if there was a way at design time to see what the form will look like 
on different L&Fs.  At a minimum, there should be a toggle to switch between the Java (cross-platform) 
L&F and the native (GTK, WinXP, Aqua) L&F.  As a bonus, it should be possible to choose a third-party 
L&F (JGoodies, Substance, etc) so that you can see what your UI will look like under those L&Fs.

The original impetus for this request came from a Java-on-Solaris discussion within Sun.  We'd like to 
see more developers using Swing to develop apps on Solaris (and other platforms as well) that look like 
native applications.  But as I mentioned above, NB does not currently use the GTK L&F on Solaris, so 
when you design a UI you will see the Ocean L&F, which will only encourage developers to create apps 
that do not fit in with the native desktop.

Related to this request, there should also be a simple option that will allow developers to target a 
specific L&F in their application at deployment time.  (Not all developers know the magic incantation to 
set the L&F at startup, or they don't know where to place it so that it gets picked up by Swing early 
enough in the startup process.)