Just wanted to report that I successfully upgraded to a 256 db install with no apparent problems. I only had a few hundred blogs, so I just wrote a script to dump them into the new tables. The install was very simple, and the site didn't miss a beat.
FYI. I'm noticing some plugin incompatiblity (not yours, lol), i'm using rs_discuss, wp-polls, firestats, wp-shopping cart, and a few others. Almost all of them had to be modified to work correctly under the db. I added the tables to the appropriate global and blog section, but the way the scripts are written, they were trying to use the wrong db. I'm hoping after a couple more days I will have all my plugins back up and running, and the confidence that my site can absorb another 20K or so blogs, :wink:.
If anyone is using wp-shopping cart, or firestats, and wants to share the changes made, I would be greatful! The others were very easy to fix, and I would be happy to share if anyone needs the fixes.