Over the past few month's I've come across many a site with this issue, and the website owner always always says the same thing ... (and its right to an extent) ... we are the brand leader, bringing something new to the market and want to be seen for x, y and z ... and to emphasise this we want it over 3 or 4 websites or sub-domains ... but we want the content to be pretty much the same... but content duplication isn't allowed by the search engines. Well ok it is true the you can be penalised for content duplication over one or more websites seen to be related, mainly via an IP address or similar domain or as a sub domain (which Google is known to treat as a different domain) ... So I here you ask how can I be saying you can do it right ... how can you legitimately duplicate content over websites and domains ... well it is fairly easy :)
The answer is "cross domain canonical tagging"
By now we should all be using the meta tag canonical - aka telling the browsers and search engines the content originates at this websites and location ... it is all your content and not taken from else where. (if not take a quick look on Google for it).
Now to use content from one site on another you need to show that you accept the origins of the content as not being on your site and being from another URL. This can be done on any element using the tag rel="canonical" - so links, images, block quotes, data tables anything with any attribute (including a full DIV) can use this tag and search engines will pick it up.
Still have questions? Please do ask them below or twitter me @andykinsey