I ran in to an issue when attempting to join a freshly reinstalled and fully patched XenServer 6.5 host back to a pool. This host was one of four Cisco blades in a chassis which had the exact same hardware configuration as the other blades. Every time I’d try to add the blade to the pool, the network configuration (which included bonded NICs) would go awry.
I recently had to reinstall some XenServer hosts and found the update procedure from both the CLI and the Xen Center application to be tedious and very time consuming. Each update had to be applied individually. Erf, not something I relished doing at the best of times. I came across this fantastic script: Citrix_XenServer_Patcher by Darren Gibbard which has saved me countless hours of downloading and installing patches on a one-by-one basis.