I have been using WordPress.com Stats plugin on my site, along with other sites that I install and manage. Lately, I have noticed sluggish page loads and tried to find the source of it. The FireBug add-on to Firefox has facilities to show what loads and how fast. Among the scripts that load was one from quantserve.com and I knew I had removed the Quantcast script with which I experimented for a while. By trial and error, turning the plugins off and on, I was able to trace the source to WordPress.com Stats. I could not find a reasonable answer by thinking about it, so I posted a forum question on WordPress.org about the matter. In several days no answer came from any source. Then I decided to do a more careful search on the WordPress forum and, sure enough, I found the answer. In a forum thread, Matt Mullenweg confirmed that they have been collaborating with Quantcast and some undisclosed features would be coming soon.
This practice disappointed me. WordPress.org and its founder Matt have been the promoters of open-source code under the GPL and stood on the side of openness and transparency. The inclusion of Quantcast script, which collects traffic information and accumulates it on Quantcast databases, with no disclosure to the users both surprised and disappointed me. What was even more disappointing was Matt’s nonchalant response “…turn off the stats plugin? :)” (his smiley)
There is a noticeable slowdown despite Matt’s claim to the contrary, I validated this on several sites I manage and all showed visible performance increase without the WordPress.com Stats plugin. Needless to say, I disabled and deleted the plugin on this site as well as several others. There are quite a few other options that provide the same or even better data. Until WordPress.com and Matt come clean on this issue, I will not use this plugin nor will I recommend it to my clients.
My recommendation to you, the reader, if you use self-hosted WordPress you should test this on your site and then decide based on performance issues as well as ethical dimensions. I learned a lesson, even the most trustworthy appearing organizations and individuals may unexpectedly behave in unexpected ways. Caveat emptor!