Internetworkers: http://www.ibiblio.org/internetworkers/

["Tony Spencer" <tony AT tonyspencer.com>]

> Hummmm, and what could I accomplish with a cookie, that I 
> wouldn't be able
> to accomplish without it?

Answer: Search engine friendly URL's

They cannot be accomplished with session ID url rewriting.  Search engines
cannot crawl your site if you are rewriting the URL with session IDs.  Maybe
traffic from search engines is not important to you but if its even remotely
important, go with cookies.  Unless you're building an intranet you almost
surely want more traffic and organic search traffic is the best kind.

Alternately you can cloak the response if you must go the url rewriting
route.  Google "cloaking" for more information.  I can show you how to do
simple cloaking or even IP delivery if you wish.  Its much easier just to
use cookies though. 

I also would not reinvent the wheel when it comes to tracking visitors.
There are companies out there making fantastic products that would take you
ages to duplicate.  Some of my favories are Urchin and ClickTracks.