The online magazine EWeek has done a review of RHEL5. It’s quite a positive review which can be summarised as “good support for Xen as service (not an appliance), better value than previous versions with the licenses for multiple guests included, and SE Linux briefly got in the way but the Troubleshooting tool fixed it quickly and easily”.
The problem they had is that the SE Linux policy expects Xen images to be in /var/lib/xen/images, but the Xen configuration tools apparently didn’t adequately encourage them to use that directory. They stored the images somewhere else and SE Linux stopped it from working. The Troubleshooting tool did something that they didn’t describe and then it all worked.
Generally a very positive review of RHEL5 and a moderately positive review of SE Linux in RHEL5.