I don't have much familiarity with testground but after some light digging it seems to be a viable tool for automating test cases with 10s or 1000s of nodes. You are able to write test plans that can assemble a test run comprising of 2 to 10000 instances, each with different test parameters, or built against different dependency sets.
This could speed up certain release tests, make them less error prone and more comprehensive.
Just wanted to put it on peoples radar. I can do some more digging myself in the near future.