Arcterex goes into many of the annoyances and security issues of HTML email (all of which I agree with). What stood out for me was the response he got to his desire to use plain text email from Scoble that amounts to "Why would you want to do that?".
This brings to mind my from a few days ago about fixing the simple stuff. I think I've come to a conclusion about the problem at MS on this - it's yet another engineering outfit where the perfect is the enemy of the good enough. Enable the firewall we ship? No, we should fix all the outstanding security issues in the next release instead! It's classic engineer's disease, and MS needs some Product Managers to step up and slap the developers silly.