Recent daily ISOs for Natty are now able to install onto, and boot from btrfs partitions. It's still very much a work in progress so ext4 is still the default filesystem. You'll have to use advanced partitioning to manually configure the partitions yourself.
Ubiquity installing to btrfs partition in VirtualBox 4.0
With this, we can expect Alpha 2 to support btrfs for testing by the community.
Error when you boot from a btrfs partition
Booting from a btrfs partition currently still gives a "Error: sparse files not allowed" but pressing any key will resume booting and Natty indeed does boot all the way to desktop.
Natty running on btrfs
It's as simple as that. No fiddling with terminal. No installing to ext4 then converting to btrfs. No need for a separate /boot partition that uses another filesystem. The only requirement is to use Ubiquity's advanced partitioning feature.