Yes. Click the little a next to the object to go into attributes and ctrl-shift click the check mark to close the window, this turns off AA for that object. It doesn't work for metaballs and trees from the tree lab. To keep these un-AA you'd have to do a mask render and composite that object into the render in an image editor. I had to do this for the tentacles in my "Refueling on Planet X" entry that's in my gallery.