It seems like you're both right. You qualified your statement with "under load". Are a majority of websites/web applications under a significant load?<p>I'd guess the real answer is that, for most websites, they're I/O bound due to the process of sending data between the client and server.<p>However, heavier applications and sites with significant traffic then require more CPU processing, thus becoming CPU bound.<p>I don't have any real expertise, but from everything I've read and seen discussed, this is my interpretation of the issue.