How much free disk space do I need to install Lion, and how much will I lose by upgrading? My hard disk is starting to get a bit cramped, with only 30GB available. I'm about download Lion and I'd like to know if I'll need to free up some space before I install it.

Also, I've read that Lion creates a hidden partition with a bare-bones copy of OS X for emergency system recovery. How large is it? How much space will I lose after installing Lion?
According to http://www.apple.com/support/lion/installrecovery/ you only need 7G of free space.

Amazingly small amount of space considering the download is 3.6G itself. 

Many are reporting gaining back between 5 and 10 GB of space as Lion is more compact than Snow Leopard.