I'm using the Web Toolkit (WTP) version of Eclipse, since I'm working on a web service. Well, another project wants to try creating a client using the Rich Client Platform (RCP), so I start messing around with that, too. Start following the instructions in Eclipse Rich Client Platform and get up to the point where you're supposed to add a view to an extension point.
Whoops. No view on the context menu. Wha? Search the web for a reason, searching, searching, nothing. Arg.
Finally discover that essentially, if you want the PDE to work, you must use the SDK versions of the packages. Yay. So it's off to download Eclipse itself, the EMF (use the emf-sdo-xsd-SDK bundle, BTW), the GEF, something called JEM from the Visual Editor site, and finally, the Web Standard Tools themselves. Fun, huh?