Are Ideas Free?

I see a lot of stories, here and on other sites and in books, etc., that have pretty much the exact same theme. Almost all of them are smut, but maybe that's just because my mind owns a huge plot of land in the gutter.

Every once in a while, I'll get an idea for a story and realize that it's been done a million times. But then I wonder if because it's been done so many times already... is the idea free to take and use? Here are a few of the MANY repeated ideas I keep thinking about.

1.) Mega rich hottie offers poor man an obscene amount of money for a night alone with his wife... maybe things go further, maybe they don't, who knows?

2.) Vixen uses her charm and good looks to manipulate some unassuming bagillionaire to fold to her every whim.

3.) Two people are intensely and completely attracted to each other and fall in love immediately. (I'm already working with this one.)

Actually, that's pretty much it.

Does anybody object to other people using these ideas if you've already used them yourself? I always wonder about stuff like this. Tell me!