This is more observational than hint-like, but it's interesting. This morning we had a customer order a new 2009 Mac mini, and they asked to have it upgraded to Leopard Server.
When we put the DVD into the Mac mini slot, we were getting ready to boot from DVD to do the upgrade. However, with this new mini, it no longer requires a reboot. You can install the Leopard Server Install Package without booting from the DVD.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090305124058230