Responding to 2) in my experience as a web developer divs are generally no longer used to round corners because the market share of the browsers which don't support css3 rounded corners is increasingly negligible.

Personally I prefer CSS3 rounded corners because they do a better job of decoupling design, functionality and content (which in a perfect world would each fit completely into css, js and html respectively).

Most developers I know followed suit with Google after they dropped support for ie7 in Google Apps back in 2011: http://googleenterprise.blogspot.ca/2011/06/our-plans-to-sup...

EDIT: Looks like rounded corners only got added to ie9 so Google's ie7 stuff is irrelevant, my guess: a degraded experience on ie8 is generally taken as acceptable.