Google Blogoscoped lists them out:
1. Our article is too long, lets split it up into many pages.
2. We have art content, so lets create an artistic navigation.
3. Lets ignore the rest of the world.
4. Lets spam everything (blog comments, email accounts, referrer stats, discussion groups etc.)!
5. Lets treat the mobile web as a separate entity.
6. Lets do a traditional homepage for our company.
7. Lets care about low bandwidth!
8. Lets read out loud the URL on TV.
9. Lets tell everyone Firefox is the better browser.
10. Lets have a tiny font that looks better.