Keith,
Deprec saved me a lot of time setting up my Rails stack on Ubuntu. It
defaults to Apache for proxying to mongrels but then I setup Nginx
separately (I’ve heard there’s an nginx recipe is in the works).
I’ve been happy with nginx for it’s lighter memory footprint and easier
configuration. English documentation is sparse but getting better. I’m
currently hosting one low traffic Radiant site – 2 mongrels about 40mb
each, using ImageMagick, ImageScience, and a slightly modified version
of
your assets manager extension (thanks!) 
– plus one other higher
traffic Rails site.
Here are some articles I found helpful.
http://del.icio.us/vcosby/nginx
http://del.icio.us/vcosby/deprec
http://wiki.slicehost.com/
The Slicehost wiki has good info on VPS setup and there’s a free
Peepcode
screencast on using deprec in there somewhere.
There’s also a new gem for generating nginx config files but I haven’t
tried
it yet.
http://errtheblog.com/post/3908
Cheers and good luck,
Victor