From what I saw at the Windows Phone 7 event in NYC there wasn't any specific tasks app. When I asked about it, the MS people suggested usine OneNote to create simple todo lists, which does show up in the Office section, and will by syncronized through the cloud.
For me, that's not only just lame, its bordering on stupid. Why are OS makers moving away from task managers? Android has nothing native and now WP7 seems to be dropping it too. Part of my life is wrapped up in my Outlook calendar, but a huge part is also wrapped up in tasks, and now I'm not relishing the idea of having to go with either 1) a crappy alternative or 2) a third-party app that may or may not work quite as well as a native app would.