How can you tell that VR works on a new lens

My only experience is with the 18-105 VR lens that came with my D7000.  I played with my new 70-300 VR lens this afternoon.  Feels a lot heavier than it looks.  My lt hand was actually getting sore.  I know I'm going to have to work on my technique but I'd say about half of the snaps I took were deleted Because they were blurry.  Probably user error but just want to make sure before I fill out the warranty card And decide   The lens is a keeper.

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Cindy