KPI’s for blogs have not been defined yet (as far as I know). Here my approach to turn web analytics data in something useful:
Top 10 KPI’s for blog
1. Average visitors per blog post (new/returning…)
2. Average comments per post (per day/week/month)
3. Number of new commentators per day/week/month
4. Number of returning commentators day/week/month
5. Everything related with RSS (new subscribers…)
6. Single access pages (drop out rate / bounce rate…)
7. Number of searches per day/week/month
8. Number of trackbacks per day/week/month
9. Number of Akismet spam per day/week/month
10. Number of Incoming links 
Feel free to add/comment!
April 10th, 2007 at 5:14 am
[...] I recently came across an interesting post from Web Analytics Book where he looks to merge web analytics (and we can easily get smothered by all the stats that are made available to us) and he links it with some Key Performance Indicators (KPIs). [...]
November 13th, 2008 at 9:31 pm
very informative post. Atleast now I have a way to calculate my blog roi with reference to this post.