[plt-scheme] running an MzScheme debugger in Emacs?

I've wanted to add tight PLT integration to Emacs, but it's a lot of 
work, and I haven't needed it enough to justify doing it myself without 
funding.  I imagine, should some organization get funding to throw 
dozens of Scheme hackers at a problem (say, to save the US from the 
subprime loan crisis), I will be pitching PLT-Emacs integration to them 
as a tools project. :)  Better yet, a bright and motivated student might 
be able to do it as a summer project.

What I currently do is develop almost entirely in Emacs with only the 
generic Quack support, since I'm much faster in Emacs than in DrScheme.  
I spend 1%-5% of my time in DrScheme, when I need a DrScheme feature.  
Every couple of years, I use DrScheme exclusively for a while, just to 
see whether it feels as comfortable and speedy as Emacs.  As for 
debugging, I loathe it as an activity, so I now make a point to write a 
lot fewer bugs than I did when I thought debugging was something all the 
cool kids did.