SEO for Web pages that require user login

I wanna know how'll search engines browse Web pages that require user login. Also what about sub-domains ? Isn't http://abc.com/sub/ better than http://sub.abc.com/ ?

Please discuss

Hi, abc.com/sub is only better because if you have enough pages you will create the "amazon effect", where many of your pages will rank highly only because they are part of such a huge site. subdomains are seen pretty much the same as seperate domains. I don't believe that any search engines index pages that require the user to login to view them.

Actually, I've had this ( half ) discussion on WebMasterWorld; there is a point: if robots.txt ( or .htaccess ) file recognizes IP ( ! ) of robots, spiders ( like Googlebot ), it may force our server-side ( PHP ) code, to let them not be asked for login. Some1 of u people, I think'll enlighten the point, I made

I don't know how this'll exactly go

the short answer is:

abc.com/sub is a better way to keep stupid search engine spiders from making mistakes, so you should do it this way.

Guide does have a legitimate point though.