Kurt,
The issue is probably that you used our “all-in-one” installer and we didn’t include the Eclipse PDE in that distribution. We’ll certainly fix that and include it in 5.5M2 and later builds. We just didn’t realize how many of our users were also plugin developers in addition to being enterprise Java developers. 🙂
The problem is easy to fix, however. Simply navigate to Help > Software Updates > Find and install… > Search for updates to currently installed features… and then select the Eclipse Project Update Site. When the wizard returns with options, you’ll see several PDE / RCP features. You should select to install them all. After the workbench restarts after installation, you’ll be “good to go”.