(Didn't you ask this recently?)
netmeg, epmaniac - After netmeg mentioned this, I checked, and yes... at first it did appear that epmaniac had asked the same question, one similar enough that I spliced the threads together. Upon reflection, I've changed my mind. The questions were different, but the titles didn't describe the questions well....
In the other thread, which had been called "Two websites in the same niche", epmaniac asked about two sites with the same content
In this thread, epmaniac notes...
All of these websites do have unique though related content?
So, I've separated the questions again and also adjusted the titles of the other thread to emphasize the important condition, of content duplication. The other thread is now called... Two websites with same content, different countries http://www.webmasterworld.com/google/4550104.htm
I should note, btw, that I do see Google ranking essentially the same content, slightly modified, in two sites owned by the same company, but it's an odd situation. The second company (a 900-lb gorilla) bought the first company, wisely leaving up the first company's site. The new parent company, after trying without success to rank for the same terms, copied some content from the first company... maybe ten or so pages... modified it slightly, and both companies are now showing on page one. The first company's content is still ranking higher, but both companies now rank on one set of niche queries. The new parent company is substantially larger, so it's not confined just to the same niche.
Additionally, the inbound linking profiles of the two sites are completely independent. I'm sure these are factors that Google looks at when allowing multiple sites to rank. In most situations I've noticed where there are multiple rankings for sites of same ownership, independence of the sites has a lot to do with it.