Crossposting

Every so often, I see somebody make a post (usually to a community) and note that it has been crossposted to such-and-such. Two questions:

(1) What's the etiquette? How miffed would people be if I started crossposting things between here and instant_fanzine, for instance?
(2) How do you do it? Nothing obviously leaps out at me from the FAQs - is it a case of people literally posting two copies of something (in which case I wouldn't bother - you want the comments page to be shared, surely...)?

Idea-A-Day

Here's a fun site: A new idea every day. The submissions range from the apparently sensible to the massively entertaining; I quite like the sense of purpose and dedication inherent in this one, for instance:

Form a rap act called 'Deathwish' whose sole purpose would be to diss other rappers, such as Eminem, Ja Rule, Nellie, Snoop and P Diddy, suggesting that they are gay. The act would be murdered in a gangland shootout and would be instantly immortal.

The site is somewhat given to hyperbole, claiming they'll provide 'an original idea every day for the rest of time.' They do this, they say, 'because it will be fascinating to see what happens when these ideas are made available to the world.' And yet, there's the terms and conditions:

By sending to IAD an e-mail setting out your Idea, you automatically grant IAD a non-exclusive, perpetual, royalty free, irrevocable, world-wide, right and license to use, reproduce, modify, adapt, publish, translate, create derivative works from, licence, sub-licence and distribute your Idea (and/or the Materials and/or the Additional Submissions) or incorporate your Idea (and/or the Materials and/or the Additional Submissions) into any form, medium, or technology now known or later developed throughout the universe.

Uh-huh.