I bought a Manfrotto 484 mini-ball head to do some widefield stuff...but the thing is that I havent really done that much with the ball head in the past year. About the only thing I have to show for it is this image of M31 I did with my 300D + 70-300mm USM III zoom about a year ago.

Although the 484 is rated for 8 lbs, it seemed I had to crank the lever down quite a bit to make sure it stayed. The other thing is that with that zoom attached it was a bit unwieldy in trying to line up the shot. Because I needed to crank it down a bit to get it to stay, it was difficult to make small adjustments in the position of the camera. Trying to hold the camera in one position while locking/unlocking was tough. You almost needed three hands (two for the camera, one to unlock).

I have no experience with the other ball heads, but if you have the money, I would go ahead and get one that has the quick release + seperate pan and tilt locks. I think it would make things a lot easier in positioning the camera, plus I think the two locks would be more able to lock the camera in place. I think the quick release would be great because you could take the camera off do a minor adjustment and put it back on instead of fumbling with things all at once.

I would be a bit weary with the mount that is on the ADM site. The site says the ball head has a capacity of 8 lbs *BUT* they show the 482 ball head which I think only has a capacity of 4.4 lbs, and I think it wouldn't handle a camera + decent sized zoom.

Don't have much to say about the dovetail stuff, I have some homemade type of stuff on my mount. Someone else would have to fill you in there