By Bryan Eisenberg of Future Now. 

Bryan has written a very useful article for anyone who is at all concerned with Web Analytics.  The 7 sins he outlines are:

1. Improper Implementation
2. No Goals Setup
3. No Segmentation
4. Paying Too Much Attention to Irrelevant Data
5. Not Setting up Milestone Events Documentation
6. Not Combining Quantitative Data with Qualitative Data
7. Not Taking Action On the Data

To see the detail on this visit his site at FutureNow.