Shared /usr in jails

[Matt Fioravante]

I want to implement a number of jails for different services on a single
box.

Since /usr is the same everywhere I'd like to just mount one copy of it
read-only to all the jails and then have them each have their own /usr/local

Someone recommended keeping the main system's /usr separate. This would mean
building a /usr for the main system and then making a copy of it
to be shared by the jails.

Aesthetics and philosophy aside, are there any real security holes in just
using the systems /usr everywhere if it is mounted read only in the jails?
THis seems to be the
approach used by solaris zones.

Thanks!