While I can easily find the binaries for the latest version of subversion (1.6) I can’t find the binaries for Ubuntu (or Debian).
The download page at tigris.org suggest to use the command:
apt-get install subversion
but as you can experience this will install up to the version 1.5.4 (at the time of writing May 6, 2009).
This isn’t a nice thing because many working copies that I share with Windows are automatically updated to 1.6 by TortoiseSVN.
You can find certified binaries here, now: http://www.wandisco.com/subversion/os/downloads?type=ubuntu910
The script will setup a repository for you, so you will keep on getting updates.