Back in 2004, there was a weird loophole that allowed SEOs to use two title tags to target two different keyword phrases for the same page. I believe that loophole is fixed and Google picks one, if you purposefully or by accident implement two or more title tags (I've have not tested this).
But what happens when you Google + stuff with a page that has two title tags in the source code?
That is exactly the case of a Google Webmaster Help thread for this web site. It has two title tags, one that reads, "Automobile Industry India, Automobile Parts, Automotive Components, Auto Accessories Manufacturers, Suppliers, Exporters" and then another that reads "Untitled Document."
So Google + uses both. Here is a picture of me adding the page to Google +:
Pretty cool, don't you think? I tried to see if I can see this page rank well in the Google search results for the second title tag, the untitled, but I couldn't get it to come up. I wonder if Google search ignores the second one completely and if so, should Google + also do the same?
Forum discussion at Google Webmaster Help.