Heather Solomon has obviously the best branding post on her blog and here she talks about rounding web parts

http://www.heathersolomon.com/blog/articles/brandsppart3a.aspx

I use a lot of XSLT and Javascript framework to modify web part and UI elements and find it usueful to not go to photoshop for rounded corners and bit of JS CSS  let you do that without image files..

here is a post of using Nifty corners as alternate for rounded webparts and other UI elements

http://cakriwut.wordpress.com/2006/11/02/moss-2007-rounded-web-part-a-nifty-corners-cube-hacks/

is it efficient.. obliviously not