5= keyword,quality,title, full description and original material
4= all of the above/ standard description /material
3= keywords and standard source like wikipedia,tv.com
2+1 rarely
the way i see it the ratings should help other users determine the quality of the content i.e. you look at 5* content first..3* can be saved for later.
if there is no description,keywords etc i dont rate but will generally comment
i think the 1* being called garbage is part of the problem with ratings..it just makes it sound so offensive.

I mostly rate 5's. I rate if I like the material. I will give a 4 or a 3 though if it is a repeat and/or bad (or no) keywords. I rarely rate a 2 or a 1, but I will if it is just bad material and irrevelant to the spot with no/bad keywords

I've actually been writing an article on this, but here's the digest version:

5 - if it's oustanding, I save it, I know that I'll keep coming back to it, and I share it with friends.

4 - if I'm really impressed by it (favorably), I might save it to check it out again, and I'd probably share the link with a friend

3 - a wide gamut, from mediocre to pretty good content, including low-res images, images that, while appropriate are not very interesting, interesting images, poorly-written articles, articles that are OK, links that are informative without being particularly impressive or well-designed/organized, articles that are good, nice images, useful links

2 - low quality images: blurry, unrecognizable (in the case of people-oriented spots), stuff that is poor content, articles which should be posts in a forum thread (short, asking questions rather than stating a point), links that point to sites with little useful or original content, videos with no sound or no visuals, videos with bad audio or visuals

1 - complete crap: Articles that are short, AND ask questions AND have disregard for spelling/grammar/punctuation; images out of focus, small, repeated; videos short, out of focus, no visuals, unintelligible audio, repeated; links that point to sites with no useful information or sites whose entire purposes is to sell something.

Edit: I've finally published my article on how I rate, in this spot.