While I have not attempted to duplicate or validate any of their individual numbers or conclusion as a whole, I have been a Drupal user for well over five years and have launched 30+ sites on it.

With this experience to back him up, he points out a few things about the report that either needed work or were misleading in their results. This includes a limitation on the web server configurations they covered, the statistics on Windows performance (might turn people off to using it on this platform) and the emphasis being put in some of the wrong places - optimizing PHP versus Drupal.

He recommends that, like all studies and whitepapers like this, you take the results as only guidelines and examples, not as absolute facts. There's always going to be differences in hardware, software and configuration so what gave the big numbers and results for them might not work for you.

As we've seen time and again, in an increasing number of enterprise software categories, open source has become a promising alternative to commercial software. But there's no free ride. Support from developers is often problematic, and you need to find products with a large enough following so that programmers have an incentive to build add-on modules. [...] Yet if you take support out of the equation, Drupal emerges as the better solution for many enterprise Web projects.

They point out some of the good (the power and flexibility of the CMS) versus some of the bad (the need for developers/admins with specific knowledge of the system) with a heavier lean towards the good. Other "goodies" they include are the robust installer, pre-integrated modules, like the Content Construction Kit and Mollom, and the ticket system built into the application for help with CMS-related issues (from Acquia).