I use Tamron Adaptall lenses on my 20D (which I received last week). I have an Adaptall 2 to M42 adapter, and then put it in a M42 to EOS adapter - everything works fine. There are two kinds of M42 to EOS adapters commonly available on eBay; a normal one with the M42 screw thread all of the way through the body of the adapter, and another kind with a rim at the bottom of the threads which depresses the aperture control pin. Do a search for "M42 EOS" on eBay Cameras http://photography.ebay.com/ and you'll often find many 'normals' and one or two 'rimmed' (no rimmed today). I have two of these rimmed adapters from DVD Technik (various eBay user names), also at http://www.dvdtechcameras.com/other.htm.
BTW the rimmed adapters don't work well with the newer ES-compatible M42 mounts which have an aperture coupling lever (see www.aohc.it/tak00e.htm) as the coupling lever touches the rim when it is screwed all of the way in - this happens on my SMC Mac Tak 50/4, and so I also have a 'normal' M42 to EOS adapter. Jim www.jcolwell.ca
