I've criticised him, and I've praised him. But, I've also learned a great deal from him.
Dr. Jakob Nielsen's Alertbox turned ten-years-old on June 1st.
If you have a web site, and you haven't looked much at usability, definitely spend some time reading through some of the articles at Alertbox.
It's lasted ten years for a good reason. Its author knows a lot about usability, he shares a lot of it, and he's a great marketer of his services. Happy Birthday, Alertbox.