There is a short list on Google Blogoscoped and a longer version on Jakob Nielsen's site.I have made so many of those mistakes on this blog that there is almost no point in correcting them now... :-)
Just to name a few items of the top 10 list:
- No author photo
- Links do not say where they go (link text such as "“here"” or "“there"”)
- Irregular publishing frequency
- Mixing topics (not becoming a niche blogger)
- Having a domain name owned by a weblog service
References:
Nielsen On Blog Design Mistakes - Google Blogoscoped
Weblog Usability: The Top Ten Design Mistakes - Useit.com/alertbox
Image source: pixelperfectdigital.com