> How at that point is it not possible to figure out that sending a PM
> to xxx will fail?
Technically, it's pretty much possible. I guess what you speak of is a default vBulletin behavior and hence remains that way. Though such things don't happen very often, it's but logical that such a check be in place.
>Basically that would really bulk up the SQL query that fetches posts
>each time a thread is displayed
Why would you need to query each time a thread is displayed? When I click "send a private message to cscgal", I go to the following link: http://www.daniweb.com/forums/private.php?do=newpm&u=1
Why at that point (after I click on the link) can't the system let me know if the person specified in the link has disabled private messaging?