Awhile ago, I ran into problems with my web hosting company. According to them, my main site (Embedded Star) was consuming too many CPU resources. It happened several times so they suspended my site. My main site has decent traffic, but not Digg type of traffic. There really wasn't a good reason why my site would consumed too many CPU resources. I figured there must be a problem with the ISP so I moved to another ISP. A few months later, I ran into the same problem. So, I upgraded to a semi-server plan where I shared a web server with three or four other people (instead of hundreds of sites on a single server). A few months later, the web hosting company again informed me my site was consuming too many resources. So I decided to get a dedicated server and put all my sites on it.
With a dedicated server, I figured my troubles were over. Wrong! Multiple times each week, my server would overload and become non-responsive or very slow. After I analyzed my web logs and removed some apps, I realized a big part of the problem had to do with all the WordPress plugins I was using. Plugins give us extra functionality, but many of us (including me) don't realize the extra load they can place on the server. BTW, even the theme templates we use can also add to the load. For instance, the old Default (Kubrick) theme generates an extra five SQL queries compared to the new Twenty Ten theme: