How reliable is the 'user' in http://user@somehost.com/???

Hi - For one of my projects I need to pass around a bit of information to all the pages. The information is the same throughout and is the same for groups of clients. Right now I just pass it on the query string, but it's getting cumbersome so I started looking into sessions and I see that I can do the $SID thing on the query string... and for some reason that reminded me that I've seen urls that look like this: http://user@somehost.com/somepath.html I've played around with it a little bit and it seems I can put whatever I want in for 'user' and that I can change it and that it "sticks" around for relative urls. And it's in RFC 1738, but it doesn't say too much. So my questions are these: - how reliable is that syntax for passing data around? - is there a reason PHP can't use that for storing $SID? Thanks! -philip