The service launched a little more than a year ago with several innovative features that effectively take over a blog's commenting system and add things like reputation, ranking, and a centralized area where blog administrators can manage comments across several sites at once.
Automattic and WordPress founder Matt Mullenweg says two of the main reasons for the pickup are IntenseDebate's e-mail replies and rating system which will likely make their way as the default offerings on WordPress.com and WordPress.org products in the near future.
For the time being, IntenseDebate has closed its doors to new users. In a post about the acquisition co-founder Jon Fox says it will be reopened to all as soon as it can prepare for a higher level of scaling. How big you ask? Like all of WordPress.org installs and WordPress.com, 4 million-plus users big.
The good news in all of this is that, according to Fox, IntenseDebate will remain a cross-platform product. From its very beginnings it has been open to other blogging tools like Blogger and MovableType. If anything, the closer integration with upcoming versions of WordPress should help accelerate development.