Good news that Windows Search 4.0 was released a few days ago. I've installed it now. The only problem is that the re-indexing takes so long time and I cannot search among my Outlook emails.
Make sure to restart after installing it.
Improved indexing performance is what I found was the best thing with the preview that I've used since March.
A useful sidebar gadget is Indexer Status Gadget.
Improvements in Windows Search 4.0 and more download packages are available here: http://support.microsoft.com/kb/940157.