Many books on presentations advise people to follow a "1x7x7 rule" — which means that we should use no more than one main idea per slide, no more than seven lines or text, and no more than seven words per line. There are many variations of this advice such as the "1x6x6 rule" or the "1x8x8 rule." Good advice? Generally, no. At least not if you are trying to have an impact. This slide below essentially follows the 1x7x7 rule, but could you imagine sitting through a series of slides like this?      

                        
This older article on writing for the web discusses how bulleted lists are, on the other hand, quite good for helping web users scan a page.

I believe bulleted lists can be very effective when used within documents such as books, research papers, or articles as well. Bullet points in a document provide easily scannable "hooks" and summaries that can improve quick understanding and lead to better comprehension. In a live face-to-face presentation, however, bulleted lists are rarely effective since it is we who should be painting a memorable picture with our words, stories, and supporting visuals. Sure, once in a while, a bulleted list may be effective in a live presentation, but usually it is best if you move those items to the handout.

Michael Bernstein, commenting on the issue of bullets over at beyondbullets.com, had this interesting comment on the topic:

Powerpoint, though, is typically a group experience, and you can use many other means to provide the audience with shared experience hooks, most importantly by using your voice....

In fact, I'd say that bullet points try to do in text what good speakers do in life....

Well said.

The aspect of the ol' "1x7x7 rule" that I agree with, in terms of slide design, is that there should be only one concept or idea per slide. This could be a chart, a photo, a single word or sentence, whatever. But it is helpful often to simplify by keeping to the "one-idea-per-slide" rule.