This is the list of incompatibilities I'm aware of (for 4.3 version):

• The design-time preview of the controls is not working properly (it doesn't render the background time cells for DayPilotCalendar and DayPilotScheduler and DayPilotMonth preview table is shrinked).
  
• When running the project on .NET Framework 3.5 it doesn't work properly inside UpdatePanel.

After loading the demo website Visual Studio 2008 asks you to convert the project to run with .NET Framework 3.5. You can convert it or stay with .NET Framework 2.0 (you can also switch later).

There will be a special service pack release coming before 4.4 to fix these incompatibilities.