How many bullet points should you be using?

• Bullets are meant to help outline concepts or list ideas.
• They are meant to be short and sweet, but tend to lean on the lengthier side of the slide.
• They are also purely text-based taking away from the visual possibilities. 
• Are you still reading this?
• Bullets can be boring.
• Did you read the first three and then jump to this one?

The answer to the title question is none.

Wherever possible, avoid using bullets. Everything you put on the screen is a graphic. Visually the eye perceives every letter, every period as a graphic. Try to limit the amount of information being put on the slide as it can take away from the oral presentation. If you want to keep your information concise, avoid putting too much information on the screen so that the slides won't look so cluttered. For example look at the following slides:

A. With bullet points

B. Without bullet points

Do you see how the subtopics are still listed in the exact same format for both slides? All the bullet points in Slide A did was just add an extra visual for the audience to look at and it doesn't enhance the slide in any way. Slide B looks less cluttered from Slide A, giving it a cleaner look. Try to avoid bullets if at all possible!