Hey folks,
This afternoon I've put together a super simple template which uses standard behaviors to achieve mouse aim (firing projectiles and focusing nearby objects). It's basically a simpler but wonkier version of FoozleCC's 3D Action Platformer Demo, which also has its source code available.
Mine simply uses the Bullet and Tween behaviors to move projectiles on the X, Y and Z axes at a speeds that are calculated using simple sine and cosine functions from 3DCamera.CameraYRotation.
Feel free to check out the demo and grab the source file if you want, I've added quite a few comments explaining what's going on.