Testing the multidb plugin and I've desided to go with 256 db just to see it in action.
I've made the change in the wp-db.php file to look at the first 2 characters of the md5 hash but I'm getting the dreaded "No WPMU site defined on this host. If you are the owner of this site, please check Debugging WPMU for further assistance." error.
Is there anything else I need to change to enable support for 256? I've also made the change in the config file with both the count and the db listing.
Working on it as well. Can't remember where that error is called from though.