Canonical planned on introducing Btrfs support in the upcoming Ubuntu release, i.e. Ubuntu 10.10 Maverick Meerkat. They even said that it might be the default filesystem in Maverick. According to a recent update in the Ubuntu Btrfs Support blueprints, Btrfs will not make it to Maverick.
Btrfs support was included in the three alpha releases of Ubuntu 10.10 that were released earlier. However, according to the update in the blueprint, the developers would not be able to complete the remaining work to make it ready in time for Ubuntu 10.10, which is scheduled for release in less than two months.
So, instead of trying to make it to Ubuntu 10.10, they have deferred the project for completion in time for Ubuntu 11.04 "Natty Narwhal". That gives them another eight months to work on it.