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Yes, it does. This is good, of course, because your iframe content will be listed in Google's results, and the links count towards PR, and all that good stuff.
The downside is that someone can visit one of your iframes directly instead of viewing your site the way you intended. The way around this would be for the iframe to check and see if it is in a frame or not (using JavaScript), and if it's not, then redirect to the home page. This way, anyone clicking on a Google search result of your iframed content will view your site the way you intended, except that they will be at the main page instead of the link they clicked.