The only thing that can expire on the forums is your "remember me" login cookie. That cookie gets renewed each time you log in. I forget what the expiration is on the cookie. Basically, if you don't access p2p.wrox.com for, say, two weeks, then the site will not remember you and you'll have to log in w/ your username and password.
Otherwise, you're automatically logged in when you access the site.
Take care,
Nik
http://www.bigaction.org/