We also have some customers using Wordpress blogs. In fact, we decided to deploy our own wordpress blog to study the case and high resource usage seems to be a daily common thing.
When you see the results under "CPU/Memory/MySQL Usage" section, you can see that domains hosting Wordpress blogs reache peaks of even 25% of CPU. The main Load Balancing is not generally affected, or at less, we haven't blogs popular enough to generate big traffic.
By now, we are deploying Wordpress 2.3.x instead the brand new 2.5, because not all the MUST-HAVE plugins are totally compatible with 2.5. Till then, we'll not recommend the upgrade. However, I have readed that v2.5 manages resource and memory usage in a better way.
BTW, you can replace ping-o-matic queries by another ones:
Code:
http://rpc.weblogs.com/
http://ping.blo.gs/
http://ping.blogalaxia.com
http://api.feedster.com/ping
http://ping.bitacoras.com
http://rpc.technorati.com/rpc/ping
http://ping.feedburner.com
http://rpc.blogrolling.com/pinger/
http://rpc.newsgator.com/
http://api.my.yahoo.com/rss/ping
Also, you may accelerate the blog using the plugin "WP Super Cache" which has done an spectacular work. But won't lower significantly the CPU usage
But hey!!! this is not a Wordpress forum!!!! 
Keep the focus boys!
