I've mentioned in the past that Firefox is moving forward on incorporating support for EV SSL into its next release. Firefox security interface designer Johnathan Nightingale has written a decent amount about his ideas for the Firefox 3 security interface, of which EV is an important piece. You can wander around his blog (as linked above) and find many things to read about usability and interface design. I'll point out a few of them here.
Johnathan's slide deck for his recent presentation at the OSCON open source summit.
A recent blog entry that explains the proposed Firefox EV interface and...