I think it not surprising that she left Google to be a CEO somewhere, it was just surprising that she picked Yahoo. Another one of those VP -> CEO jumps that was interesting to watch was Ed Zander (Sun Micro -> Motorola).
What I was expecting was that she would leave and start some sort cross between 'solve a world issue' with 'easy accessibility' kinds of UI. At Google her strength was having a clear idea of how to speak to users through UX, The Yahoo gig can use that, certainly, but watching the succession of failures and missteps at Yahoo the issues aren't primarily UX or users, it seems like Yahoo is in a major identity crisis about what exactly it actually is.
When one of their recruiters was trying to convince me to join the pitch was this:
"Yahoo is the premier digital media company
Yahoo! delivers amazing personalized digital content and experiences, across devices and around the globe, to vast audiences. We provide engaging and innovative canvases for advertisers to connect with their target audiences using our unique blend of Science + Art + Scale."
To which my response was "Really?", if someone were to ask me what the "Premier digital media company" was I don't think I'd respond "Yahoo!"
Hence my surprise.