There are two ways to import models from Blender into Unity:
1) Export manually from Blender and then import that FBX file in Unity. That should work just fine with Blender 2.5, or even better than Blender 2.49, because I believe that they fixed some problems/bugs.
2) Drop Blend file directly into Unity and expect Unity to do the conversion. This doesn't work, because Blender 2.5 is in still in beta phase and python scripts do not work properly in default Blender installation. As soon as issues are fixed on Blender side we will make sure that integration with Unity works.
I'll update this thread once I have more news.
If you want to ask something you can do it here:
http://forum.unity3d.com/threads/618...nder-2.54-soon
