This network location: pppox pool se12.emhril 121307 0145 gave my website between 500 and 1500 on each of the days May 10, 11, and 20. Each visit lasted less than a second.

For perspective, my sites gets about 100 unique visitors a day.

Nothing suspicious has been seen except this information from Google analytics.

Any thoughts? Is this a spider of some sort??

Thanks! By the way, my site is a free site that members can signup and get stock market news, etc.

Hm, sounds like some kind of robot/spider. Could be an automated security check. If it continues to bother you, I recommend checking the raw HTTP logs, to see what it does, and if it's unwanted activity, ban the IP. Redirect it to 127.0.0.1 or something for laughs.