I showed recently Google will use the next available Header, be it a H1, H2, H3, H4, H5 and H6 if your page title element is screwed.

The snippet below shows Google using a H6 header as the page title.

http://www.hobo-web.co.uk/seo.html

Yahoo will actually ignore the Header tags on the same page and elect to use the anchor text of incoming links

Yahoo

MSN / Live seems to just go for it, and index the title as much as possible (@ 75 characters?)

MSN

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