Well I've been playing around with it this morning and am getting the unavailble message as well. Although I imagine everyone is hammering it. For me first positive that I have found is the increase in the number of pages cached. I look after 2 sites both with v-bulletin forums. Results as so. Current MSN Site 1 has 3,671 pages and 3 from the forum. The Beta version has 4,301 and 217. Site 2 current MSN has 50 pages, Beta 705 and 4 forum pages vs 3,838 Although haven't checked on the search term rankings, more pages in the index has to be a good thing.
i looked at beta.search.msn.com it's different from the techpreview.. full release will be end of 2004 news.bbc.co.uk/1/hi/technology/4000015.stm
It works for me... it just takes 11.66 seconds for a query and returns only 1 result. They probably moved it to some Windows machines running SQL Server.