Thank you - and very happy to receive a longer answer than my question!

That certainly answers my basic question, and I really appreciate it.

What do you think about the more "semantic" tags of HTML5 - such as the "nav"? Surely it's a good idea to use them to help Google (and later web developers) on their way with understanding the structure of the content?

And, a related question, can and does Google read CSS files to determine structure too? It's not mentioned on the blog post you pointed me to (and thanks for pointing me to it - a very helpful article in all sorts of ways which I hadn't read.)

I read/was told that it was a good idea to order your HTML to show the most important content first. So, on many sites I had put my global navigation div, for instance, below my main content div. Does this still apply? And does wise use of HTML 5 mean this is no longer necessary (eg use of "nav" section tag to indicate this section is about navigation).

In the same vein, how does Google know that my sidebar nav is my sidebar nav (which your site seems to say is probably given less weight than top nav), and how does it know my topnav is my top nav? Maybe a daft question, but when someone asked me yesterday I realised I didn't know!

(Phew - at last I have asked a short question!).