What are anti-spam measure I should consider before launching my user content website? Some things I have considered:

• Silent JavaScript based CAPTCHA on the register page (I do not have an implementation)
• Validate emails by forcing a confirmation link/number
• Allow X amount of comments per 10 minutes and Y per 2 hours (I am considering excited first time users who want to experience the site)
• Disallow link until user is trusted (I am not sure how a user will become trusted)
• Run all comments, messages, etc. through a spam filter.
• Check to see if messages are duplicate or similar (I may not bother with this. I'd like the system to be strong without this)
• I also timestamp everything which I then can retrieve as a long on my administrator page.

What other measures can I take or consider?