There's one fix I wanted to point out as I am transition over to using Rails 3 and using the new Passenger 3 modules. This blog post does a fairly good job of talking about setting up the whole scenario but there is one glaring omission: make sure the append a final "/" on the 2nd URL you specify in both the ProxyPass and ProxyPassReverse statements.

ProxyPass / http://127.0.0.1:3000/ 

ProxyPassReverse / http://127.0.0.1:3000/