Elgg multisite discussion

Some experiences are mentioned about the Elgg as a multisite. Some plugins are avaliable at Elgg plugin space ("multisite" and others).

How you see the use of Elgg as multisite? One BD and one core (racked from original)? Or  multi BD and onde core (racked)?

Any "benchmark" avaliable?  Could we call the Elgg multisite a system "like NING"?