Mmm, multiple cookies might be the best cross-platform solution (from the board operator POV) - however you need to consider 2 additional factors:
a) Cookies - The browser will have to send every cookie back that it received in the past 10 minutes - introduces request latency.
b - and a BIG b) HTTP RFCs state that a HTTP Request size is a maximum of 4KBytes in size. Now I'm guessing your cookies are small bytewise in value and smallish in name, but remember you have a 15 character overhead for each cookie.
This means that you can quickly overflow the max request size if you are reading posts or flicking through a forum.
Compounding this issue is that users of Checkpoint Firewall 1 (i.e. big business) default HTTP Request size is 1KB.
In summary, it's the easy way to do it, but will introduce big problems for many users.
Hope this helps.
Clarify - this is HTTP Request _HEADER_
Paul.