I have seen this, very interresting Susan. The only problem I am having with using libraieries other than script.aculo.us is the risk of incompatibilities. Since QuickEdit requires script.aculo.us, if moo.fx breaks it, that’s not good...
I have done an Ajax enhanced login box with script.aculo.us for a client’s website, using effect appear (can’t show it, since it’s not live). I did not touch the Weblogin snippet either, I just placed the code inside a hidden div with a js link, also providing an alternate for those with js disabled. This being said, it’s probably a "quick and dirty" solution, and if I could be sure nothing breaks QuickEdit, I agree that moo.fx is lighter and probably the way to go