I have a solution: xargs
Xargs walks on water. It is incredibly useful. In a nutshell, it runs a single command on a list of files. I'll post a lot more later, but here's how to speed up apt-get:
apt-get -y --print-uris install ubuntu-desktop^ > debs.list
egrep -o -e "http://[^\']+" debs.list | xargs -l3 -P5 wget -nv
apt-get -y install ubuntu-desktop^
Replace "ubuntu-desktop^" with whichever task or package you want. Since ubuntu-desktop is a task, a huge collection of packages, the "^" on the end is required (and magic).
The options say to take three packages into a batch (-l3), and download five batches at a time in parallel (-P5). These settings are arbitrary, but provide a nice speedup while also not hammering the Ubuntu repository servers too hard.