Since setting up my development environments on Mac OS X Lion (brand new macbook air purchased in January 2012), I have noticed that resolving to a virtual host is very slow
I had the same problem, also on Lion.
Strangely, my solution was the opposite of Jeremy's. I had a whole bunch of someproject.dev entries on one line in /etc/hosts. Loading a site on any of them the first time took forever, like a minute or so. If I used it again within 5 seconds or so it was very fast, but much longer and it would again take a minute. I had suspected all sorts of things, mysql connections, Ruby versions, Rails bugs, Apache, Phusion Passenger. Until I finally looked at the Console and realized that DNS lookups were being attempted.
So, I put all of them on seperate lines:
127.0.0.1 localhost
127.0.0.1 myproject.dev
127.0.0.1 myotherproject.dev
And suddenly everything was snappy again. Same on both my machines.