Also, this may be a completely separate issue, but shouldn't persistent cookies set over https also be encrypted on disk in some way? If a bank website was found to be setting persistent cookies over https, i'd sure want the browser to be encrypting that cookie in some way before putting it on my hard disk. Again, I don't know if browsers already support this, but I think they should.
Yes, but how many web developers are in a position to decide how their documents are cached, and of those, how many care to? If it's in the web browser I can determine how sensitive data is handled so I don't have to rely on all web developers to do the right thing.