There is nothing wrong with any of the instructions. Not only this, but I was able to share the 'sessions' table and now all users are actively shown on both sites.
The good news is it's working.. just like I thought it would.. the bad news is it's way to early to tell if anything will or can go wrong.
Also, since I'm not having a problem, and I'm also on a way older version of VB than described in this hack, just to let you know.... #8 the $idname hack info above for a certain function didn't even exist!
Not only this, my search and replace couldn't find any " . TABLE_PREFIX . "strikes either. When in doubt, the only thing really required is review of your SQL statement. When the author says replace " . TABLE_PREFIX ."user with "."user he really means replace it just like that.
I will mention another thing that puzzled me, if you notice, the author is using some special "quote" around his periods in the tutorial above. In my case, it appeared like block characters in my Search and Replace function so I just replaced the funky `` quotes into single double quotes surrounded by the period. ie: "."
Regards,
Peter