I would like to offer some of my content to other users that they can put on their homepage. I plan to use a Iframe.

I know that google does not like to see the same content on several sites, and I do not wish that my contents get indexed as part of some one elses homepage.

Now my question is will google read the content of Iframes as content of the site the frame is in or as content of the url the the irame point to?

and I do not wish that my contents get indexed as part of some one elses homepage.

Then don't offer it out.

Content in an Iframe will be indexed as the page specified in the src attribute.

Google doesn't follow iframe SRCes. For the content of an iframe to be crawled, a link to it is needed somewhere, and between the iframe open and close tags is good place to put it.

actually they do follow the SRC attribute. The only place this result is linked from is the iframe src.

Google shows no result(s) for that search. But if they indexed the iframe src page, then it must be something new. I tested it earlier this year by placing an iframe on the front page of a site that is crawled every day, and I left it there for months, but Google never crawled the page in the iframe src.

They crawl frame SRCes. You're not mistaking it for that are you?

<added>
Correction: now I see the result. It didn't show the first time.