This wiki page on using SELinux with Ubuntu informs of the following:
The Ubuntu-specific "selinux" and "selinux-policy-ubuntu" packages documented here have not received much attention since Karmic, and appear to be effectively broken in Precise.
So does it make sense to even consider installing SELinux with the purpose of making a general-purpose Web server running on Ubuntu 12.04 more secure? What are the potential problems that SELinux can bring into an Ubuntu Web server?