Conduit, currently an Fxplug for Apple Motion and Final Cut from dvGarage, is coming soon to After Effects (and Photoshop) for both Mac and Windows. Conduit gives you the basic nodal compositing functionality of Shake, and on the Mac it works in real time through GPU rendering. It's especially useful live on greenscreen sets, letting you adjust lighting setups and capture live 4:2:2 color through HDMI from HDV cameras like a (now) $600 Canon HV20.
Features on Windows for the AE filter will be limited compared to the new Conduit Suite on the Mac, since leveraging Mac OS APIs makes so much possible so cheaply (compare pricing with the new and less capable FXhome filters). Details on the release should be finalized in few days.
Much more info and explanatory movies on Conduit and nodal compositing can be found in the demo section of dvGarage Conduit pages, and on the blog Lacq’ing in Depth.
Update: There may have been confusion about inequality of features across platforms, after all my source was an a little card from the Macworld booth. The developer for Conduit for the Window side made some clarifications in the Comments section (click on post title to access). I think the difference is that Conduit Suite, which includes Conduit Live, is only on the Mac. The AE filters and file formats are the same.
Update: Details on the release should be forthcoming January 30.