@mnpumar: There is a separate library that Elco wrote that does handle 2D led matrix. I believe this could be easily modified to run as a 3D cube. (ShiftPWM support topic. Latest update: Schematics, high power LED's, LED strips - #88 by system - LEDs and Multiplexing - Arduino Forum)
There are limits on how many LED's you can address and if you are using a standard Arduino (328) the limitation is the array size (memory limitation). But if you were to use a MEGA with more memory I believe you could go beyond that. Currently with a 328 Arduino the limit is 1024 Leds. I currently have this many Leds running in a 16x64 single colour matrix. There are a number of other variables that influence how many LED's you can address (Frequency and Brightness levels) vs the speed of the arduino.
I am not sure if 10x10x10 RGB would be feasible....that would be 300 LED's per plane of the cube, with 10 planes that would be 3000 LED's that would need to be addressed total. I just don't know if you could do this at a fast enough frequency to not have flicker......
But that is not to say don't try. Would be very awesome to see!!!