I'm having a problem similar to what "sertac" posted. I have eight or so .lyr files that I can bring into ArcGIS Explorer (build 1500) and zoom around in 2D with no problems. If I load only one of the .lyr files into my map, I can switch into 3D and it appears to work fine. If I load more than one, it hangs ("not responding," no CPU cycles, needs Task Manager's End Task to close).
I'm using an almost-new Dell workstation with a high-end NVIDIA Quadro graphics card (yes, just updated the drivers today), running Windows 7 64-bit. The data is all coming from the same file geodatabase feature class, with the .lyr files having definition queries, scale extents, etc.