FWIW, I've hacked together a Fedex Channel for Sherlock 3. Even IMO, it pales by comparison to the Watson Packages plug-in. That said, Sherlock has the advantage of being built into MacOS X.

I haven't done any Watson development, yet. (I'd like to give it a shot and compare it with Sherlock 3, when I get the time.) As noted above, Victor Ng has great notes on his experience with the SDK. As Victor notes, the most frustrating bit has to be the complete lack of feedback for even the simplest syntax errors. The developers of Watson have a brief, but informative comparison of the two SDKs, as well.

what are you talking about? There is an active community in the sherlock-channel-dev mailing list.