I stumbled upon this when testing JBDS on Leopard:

When you install the Cocoa (32bit) version of JBDS on Leopard, it lets you install it with no problem even though it's not supported because then it's bound to run with Java 1.5 (Java 1.6 is 64bit-only on Leopard).
When you start JBDS after the installation at first everything seems ok - the welcome screen, the menu... But for example the installed EAP runtime is missing and soon you realize that other plugins are missing too - this is the result of running JBDS running with Java 1.5 in this case.

If a user installs 32bit version of JBDS on Leopard, it is his fault. But it would be nice to have some kind of warning - either during the installation. Or when JBDS is started with Java 1.5.