I also think this piece of code
Content visible to verified customers only.
Should actually be part of vb3.php's procedure "update_whoonline" as it's only used once. The "600" should be a control panel option imho, as this "session timeout" can be changed in Vbulletin .
Finally, ipaddr is defined as a varchar(75), not sure why (might be a reason for that), but an IP cannot be bigger than XXX.YYY.ZZZ.WWW (15 chars). Okay it's a detail
Just a couple of suggestions.