In no particular order.

1. You don’t list your full name
2. Incomplete profile-for example you only the title of your current position
3. Out-of-date profile, congrats on that promotion 10 years ago, what have you done since?
4. Too much personal informaton
5. Too many status updates (don’t care that you just took a phone call from an important client)
6. No status updates
7. Restricted profile access
8. No responses-invites, articles, etc.
9. Only using your profile to pitch some sleazy service or product-apologies to legitimate users
10. Spammers, freaks, and other weirdos that try to connect.