Well, I am a user of Allplan for fifteen years or more and I can say Allplan is a great peace of junk. It's very expensive, it's complicated und there is only a rudiment of a virtual building. The best about Allplan is the money they spend in advertising.
So, why I'm so rude? Very easy! Yes, you can build a virtual model and feed it with data. But all functions to get a benefit out of your model are only half developed. There are a lot of known bugs which are not fixed for years and after a main release there are certain new bugs in functions, which worked properly before (e.g. in version 2008 the dimensioning tool was fine, in version 2009 it took a service release to fix it). In the german nemetschek allplan forum are a lot of dissapointed users. They all stay with Allplan, because they paid so much money (and my boss, too) until now and they all HOPE that the bugs get fixed in the next main release. From my point of view I can say: Allplan is far away from a modern BIM-based CAD. The only usable and payable BIM-based CAD I know are ArchiCAD and Revit.
Torben