"the fact remains that AD is a huge powerhouse in the enterprise"
Huge powerhouse in the enterprise? You're in fantasyland.
The author does not know what he's talking about when it comes to Directory Services and should do some research (unless he's an MS shill) to re-write the article. Novell has over 1 billion licenses in the enterprise, is the fastest growing DS in the market and is multi-platform with 10 years of evolution behind it.
I know personally of 3 multi-billion dollar companies who looked at AD and decided against it due to either immaturity, cost, or lack of functionality....they're sticking with eDirectory and DirXML. Most "enterprises" are multi-platform and cannot migrate completely to Windows (2000 or 2003 server, 2000 or XP desktop). AD is not a "powerhouse" and is more often avoided than not...people would even rather stay on NT 4 domains (even when unsupported) than try to move to the immature bloatware that is AD. Just look at the extremes MS is going through to get people to migrate off NT4 (they extend support, they make upgrade offers, they're re-writing Licensing 6, etc.).