I'm having trouble upgrading too, and would love some help.

I'm using Ubuntu Hardy, and tried the following:
1) Downloaded Jake's public key to a local file (my machine is behind a corp firewall and couldn't access keyserver directly)
2) Used apt-key to add the key to my machine (had to apt-get gnupg first)
3) Added Jake's URL to my sources.list file (it was under /etc/apt/sources.list.d)
4) Tried apt-get update
5) Tried apt-get install nginx, but I was told it's already up to date (with v0.5)

I tried following some of the other info on this thread, but I don't have aptitude installed and if I can get apt-get to do the same, I don't want to install it.