reprint - 3:44 pm on Jan 8, 2009 (gmt 0)

I havent paid attention to this thread in a while. Yes, there are certain plugins and themes that are not WP MU compatible though I am finding less and less. WP MU is less intuitive at first than plain old WP but once the initial learning is done, its a breeze.
If you have installed WP 2.7, then go to Tools and under there you will see Upgrade. This is supposed to be a one click upgrade for WP. Since there havent been any releases since 2.7, I havent seen it in action yet. WP MU 2.7 should be out end of Jan or early Feb by current estimations though not sure yet if one click upgrade will be incorporated.