Top 10 Usage Blunders
(according to the editors of the Microsoft Encarta College Dictionary)

1. Misuse of there; confusion of there/their/they're
2. Confusion of affect and effect
3. Spelling a lot as one word
4. Confusion of fewer and less
5. Confusion over placement of the apostrophe;
6. Misunderstanding of it's/its
7. Confusion of blatant and flagrant
8. Use of would of, etc., for would've, etc.
9. Inappropriate or excessive use of the passive voice
10. Using like as a conjunction
11. Use of relative pronouns with vague, inappropriate, or nonexistent antecedents