I think I read that Arkose be installed by default in 11.10 somewhere on the Canonical blog.
If you don't know what it is, see http://www.stgraber.org/category/arkose/
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Arkose is in the repository since Ubuntu 11.04 and the all latest release is currently in the Ubuntu 11.10 repository.
Unfortunately Arkose won't be installed by default in Ubuntu, so you'll need to install it from the Software Center.
It's part of the default Edubuntu install though so if you're looking for an Ubuntu flavour shipping with it by default, there it's :)
I also usually backport any new version of Arkose to Ubuntu 10.10 and 11.04 in the Arkose stable PPA: https://launchpad.net/~arkose-devel/+archive/stable
I'm also trying to push the use of Arkose and similar technology for apps available in the Software Center post-release, like these going through the Application Review Board and through the commercial process. This isn't the case yet though but might be in the near future. In such a case, Arkose would become a dependency of any package requiring it and would be pulled on your system when installing one of these apps.