I have made some significant change in the multiple site functionality, as I was not happy with this solution to use the site title as the id of the default site.
So I changed the 'show_copy_site' settings entry in 'multi_site_func' of the type integer. If the value > 0 then it is the site id, if 0 (or unset) then the functionality is off.
I did use a the session variable 'multi_site_func' for it (instead of the settings class as discussed) for the moment as that is what we have done and not sure if we finished the discussion about the amount of extra database overhead a lookup every time would cause (or did it not?). I checked however that a straight replace should be possible and this can always be changed later if needed.
I updated the UpgradeQuery.php file to reflect the change, but please be aware to make the change manual (e.g. show_copy_site (bool) to multi_site_func (int)) in your table.
Sounds good. Eventually, it would be nice for the sites thing to be a drop-down. I'll answer the settings question in the thread where we were talking about that.
At some stage (after college is over, if somebody reminds me) it would probably be good if I write a bit about this functionality on the wiki I think, as it is something that otherwise might be obscure or a functionality that is unknown for the bulk of the users