If my directory got spammed I would HATE to get 100's or even 1000's of emails within a matter of seconds, minutes or even hours. I think it is a BAD idea to do something like this. One solution could be what Fredto suggested:
New link(s) submitted since last login: X links (Check link(s))
Alternatively, a daily/weekly/monthly email could be sent out with a summary of stats with the number of links in the queue; this seems more plausible IF you would want email notifications at all.
I also believe that the auto approve via META or HTML file is a BAD idea. Expanding on what Pavel said, it would lead to misuse, exploitation, etc.
Personally a quality directory has an owner who reviews the website for quality links, not spam sites, or other malicious websites built only for making money etc.
Also, another idea may be... On the listing of sites awaiting approval, there could be check boxes which would allow you to bulk approve... And in the configuration you can either set "Auto Spider Upon Approval" to on or off. If it is on, all approved listings would be placed in the spider queue and will be crawled in order added to the queue behind the scenes (meaning you do not need to watch the crawling).