Fw 4.5 (109) appeared on internet on April 4th 2010
OpenZDK appeared on internet on April 16th 2010 (zuneboards site)
So it was safe to upgrade, but becareful in future, because it may be easy for MS to detect and block unsandboxed apps (OpenZDK allows native arm code outside of xna framework)
Thus, that's one more mobile device able to use OpenGL ES 2.0 (like iPhone 3GS, iPod 3G -i.e only 32/64Gb fast models-, iPad, Pandora, Google Nexus, etc...)
Doom is probably the well known software based 3D version.
Cubic, on the other hand (get it from same source), is a nice 3D rotating textured cube sample (sources included) that really shows the speed of accelerated 3D through Open GL ES 2.0.
(launch Simple\deploykit.exe from the cubic archive to install it)
Rotate it with your touch, zoom in or zoom out with two fingers.