Boxes and Arrows have published an informative article examining how common design elements on popular e-commerce sites have slowly become something of an unwritten ‘de facto’ standard.
This is something Steve Krug touches upon in his book “Don’t Make Me Think!” – at the most basic level, people expect the top left of a page (or at least a corporate logo) to link them back to the homepage of a site.
The article contains a few more examples, but you get the idea.
Couldn’t agree more re “top level logo” being linked to home pages. A whole load of users have learnt the internet in the last 12-18 months, this is a given now IMO/IME.
Most browsers have their nav buttons top left – I think that also plays a role.
Safari has it’s awesome “snap back” feature that does similar (returns you to the page you entered on/at).
PS – not sure if you’re after random comments, but you got one just in case!