Stephen adds: "Speed Doubler 8 also does not support fast copying using contextual menus, although Connectix promises to provide this capability in the future."
Update: Julian Yip-Khoon Koh, who has written a review of Speed Doubler 8, claims that file comments do survive a copy to another disk. Well, I just got my copy of Speed Doubler 8 today and I tried it. The comments were definitely lost for me. A bit of detective work (by Julian) revealed that the comments are lost if you are using Mac OS 8, but are preserved if you are using Mac OS 7.
Meanwhile, a possible work-around for this problem is to use Commentator, a utility that can extract comments from one drive and restore them to another.