Client has a dating site and would like to have a popup (either a nice javascript overlay or a new browser window popup. we're flexible.) displayed to users when another user is visiting their page.

I'm familiar with push technology and Comet but it's quite challenging to implement this and may place serious strain on a server with over 100,000 unique visitors per day.

I'm wondering if there is a way of faking this, perhaps by not being accurate to the second. I can't really think of any way.

This is a classic LAMP environment.

Anyone?

EDIT: what about this: placing an iframe on the page that refreshes every few seconds and at each page load it checks in the db if a visitor has been logged on this profile page. if so, it shows a message. the message would be visible but the background of the iframe would blend in with the background of the site and be invisible. if the message fades in and out, it would look like a JS box "popping up".