Well, after my enthusiastic post, I must say it is not a "good work" after all. After replacing the app itself and launching it I discovered that not only MC did not take over my registration info, but it also wiped the current preferences file, removing all entries! This is certainly not a smart thing. Thankfully I backup my Mac every day, so I was able to restore version 2.1 and all prefs and plists to get back to where I was before. But if you have not backed up, be careful and make a copy of the preferences files before you upgrade. Thumbs down, I am afraid!
Paolo