Our company is still using a single subversion repository tree for all our projects with the following classic structure.

root
--elcs
----trunk
----tags
----branch
--hcs
----trunk
----tags
----branch

One disadvantage of this setup is that all projects are sharing the same revision number which is shared across the main repository tree.  We're using the revision number of our subversion tree as part of our projects assembly version (MajorVersion.MinorVersion.SubversionRevisionNumber.CCNETBuildLabel) so the third number does not really imply the number of revisions that the said project had undergone.  This is one of drawbacks of having just a single repository for multiple projects.