This is a great list of the 10 Social Media Myths. Quite a few I have heard myself, too:

1. Great Content Always Goes Hot
2. There are No Rules
3. You Can’t Build Quality Relationships Online
4. The More Friends, the Better
5. Social Media Marketing is Easy
6. Social Media Won’t Last
7. Social Media will Replace Traditional Marketing
8. Social Media is a Cure-All
9. Social Media is for Kids
10. Digg is All that Matters

Go to the site and read it, it’s great stuff!