A big shout out to Caleb Pike, who turned me on to the whole FD lens on HDLSR thing. Picked up some inexpensive lenses on eBay and have been testing them out with my 600D (a.k.a. the Rebel T3i).
This first sequence was created by setting the ISO at 100, then stepping through the aperture range from open to closed, and varying the shutter speed to achieve a neutral exposure per the small in-viewfinder scale.
You'll notice the overall exposure varies slightly. This is a result of the too-simplified scale in the viewfinder. To properly control exposure requires more monitoring than this.
You'll also notice how dramatically soft the lens is at f/1.8 (just as Caleb pointed out in his overview). Stopping down the lens sharpens it up quite a bit and still delivers a usefully shallow depth of field. As the lens is stopped down further, the depth of field deepens and the overall sharpness of the image improves.
View it in fullscreen to get the full effect and see the details.
The adapter adds another layer of glass to the system, which can flatten the colors a bit, and also makes this 50mm lens equivalent to about a 63mm lens (1.26 factor).