In 2006 I helped create an omni drivetrain for team 859 using the poly AndyMark omniwheels, only to have the roller mounts (around the circumference of the wheel) shatter several times on the ramp. Other teams had better luck with small caster-style wheels such as from omniwheels.com or mechanum (angled roller) wheels.
At least without ramps this year's game should be easier on omniwheels.
