I have found these interesting articles about common mistakes in web design.It's really useful reading.
The ten most egregious offenses against users. Web design disasters and HTML horrors are legion, though many usability atrocities are less common than they used to be.
Design Tips : 101 Common Mistakes In Web Design
Top Ten Mistakes in Web Design
9 Common Usability Mistakes In Web Design
50 Common Web Design Mistakes
43 Web Design Mistakes You Should Avoid