and here is some free-as-in-beer RPC 1.1 stuff:
http://www.opengroup.org/products/publications/catalog/c706.htm
And on there, they just want to borg the email addresses of every reader, but not their souls or firstborns, as far as I can see.
When they set up this 'free' access to the documents it was rather a change of direction for (what was then) X/Open. After all they had a business model that assumed they would be making money from selling the books, rather than just taking money from the contributing companies and giving away a 'free' copy of each book to each company.
In any case they wanted a log of who was downloading stuff, but they said at the time that the email addresses wouldn't be used for other purposes. I've certainly never received junk mail from them.
I suspect the log (like the ones from anon ftp passwords) is of little use to anyone.
David