As someone who until recently subscribed to Weight Watchers, I can confirm this is good news. Even with so many fitness trackers on the market, WW still has a best-in-class food database; it's simply more comprehensive than anything Fitbit or Jawbone has to offer. And, you know, the program works. That's why people pay for it. But food-logging regimens are harder to follow faithfully when you have to manually enter lots of data and indeed, it can be annoying to type in my 35 minutes of running, when I already logged it with Jawbone.
Ideally, the integration with Jawbone, etc. would be two-way: Weight Watchers would share your food log, to make up for the fact that Jawbone and Fitbit aren't as good at recording your food intake. Also, since Jawbone and Fitbit both work with WiFi scales, it would be nice if those apps could send your weight straight to Weight Watchers so that you don't have to log it manually. Alas, though, the connection is one-way-only, with Jawbone and Fitbit sending your activity data to Weight Watchers, but not the other way around. Which makes sense: Weight Watcher's food database is its crown jewel, and I can see why it doesn't want to share it. But Weight Watchers is a weight-loss program first, and a technology company second; its app isn't as polished as Jawbone or Fitbit's. To let users bring their WW data into a different app would make for a more pleasant user experience.
For now, at least, Weight Watchers will only pull in data from Jawbone and Fitbit, though Weight Watchers says support for other devices is coming soon. Both apps are available for iOS and Android, with iOS 8 support coming soon (iOS 8 doesn't even come out until next week).
Also, because the integration works with the help of Apple Health for iOS 8 (available next week), this feature will only available on iPhones and iPads. Weight Watchers declined to say if an Android version is on the way. In the spirit of choice, though, we hope it is.
Update: Looks like we were given some incorrect information. The integration with Jawbone and Fitbit will indeed work on both iOS and Android. Updates to both apps are available now. Go get 'em!