Might be a dumb question but...

[AdrianR]

Is it normal for the rear differential to get warm, or even hot to the touch when the bike is being used?

Thanks!

[goldstar903]

Yes, it's normal.  Try not to touch it while riding. Touching while riding could cause an accident! 

[Robert]

Yes and one of the easier ways to tell if that new rear end oil you put in actually does anything. All things being equal lower temp equals less friction.