Register Globals should never, ever, ever be used. I don't know of any specific problems it causes with Drupal or Ubercart, but that doesn't matter. It's such a terrible idea to have it on that I'd blame all your problems on it until proven otherwise.

As for Workflow-ng 2.0, I haven't had any problems with it so far. The changed path structure still throws me off, but that's just a retraining issue.