I stole Theo Heselmans' idea (see comment 4 in related idea) thus this could be voted on separately from Ben's $ 1000 idea.
Let the user not only Promote, but add a weight to the promotion: 1 for "OK, but not that important to me" to 5 (or 3) for "Great, very important to me"
The user interface could be relatively simple: 5 (or 3) stars. The left-most star is just one, the right-most 5 (or 3). If you hover over a star, this star and all left of it are colored different. (see rating in Blogsphere 3.0b8 for a implementation or have a look at our blog: http//www.assono.de/blog/ )