I wrote about extended validation certificates in 2008.  What's changed?  Well EV certificates are generally cheaper and there are more providers.

If you think your customers/clients are very concerned about the privacy of their own data, and ensuring the identity of the website, EV certificates should probably be used.  If "ecommerce" simply means "selling goods" I would examine what your direct competitors are doing.  It's quite likely EV certificates will become more popular, but you can always upgrade very easily at any time in the future.  Do make sure SSL is configured correctly on the server, and the application uses it correctly - avoid common problems.

And, if it's a new site, or an existing going through a major upgrade, seriously consider the whole site being SSL nowadays.

Oh, the email notification didn't work. Thanks for your replies!

There is, in deed, one major and successful competitor using EV, but it's just one and it feels an expensive price to pay.
I'm with the commentators on the McAffee Trustmark. It brought us a mere 2% improvement on their own A/B test. Obviously, at least something, but nowhere near the tempting 9-12%.

Merely trying it for a your might be a bit tricky as well. It mighte create more problems when the "green bar" is suddenly gone than not having one in the first place.