I've always figured that with so many webmasters wondering about their rankings, position checking software must make up some noticeable chunk of the queries search engines receive. Indeed, it's possible that some popular terms are so "popular" in part because webmasters vying for position are constantly running queries to check on their rankings. A recent post from Northern Light's CEO David Suess sheds new light on the topic. In a message to members of the I-Search mailing list, he said users of WebPosition Gold generated half a million queries per day at his service, before the software program was recently blocked. Suess says that other robotic query agents are also blocked if they have no agreement in place with Northern Light.
I-Search Digest #252
To see the comments, go to the link above, click on September 2000, then select issue #252 and look for the "NL Block" post.