You should be using NewRelic by now, but you might not be checking out their blog regularly. They feature a constant stream of news relevant to the entire developer community, not just their customer base.
This week their blog features an article about the permutation testing they go on their Ruby Agent, testing it out against various Ruby versions, Rails versions, Sinatra versions, and other popular third-party gems. If you are looking into testing permutations, this is definitely worth a read!
And as always, NewRelic is still awesome and accounts are still free. go get one at newrelic.com