My method
Redraft - how well and how consistent will the player perform in 2008? I take into account overall upside and risk, but I am real big on “consistency”. My method has always been to draft (usually) the 'safest' players. I figure I will do fine if I have a bunch of guys who consistently score above average, rather than a bunch of guys who do fantastic one week then disappear the next week. A RB who breaks 10 points every game is, IMHO, golden to me, and I'd rather have him than a guy who will break 20 points 5 weeks in a row then disappear (or get injured) for a long stretch. Team situation is huge, i.e. a team that relies on a player to do…something…gets huge points in my book even if his talent level isn't tremendously high. A guy like Addai who is a good RB is barely a top 10 talent, at best, but because of his situation, he gets huge points. I think Willis McGahee is another one who isn't an ideal talent but is definitely in an ideal situation. Contrast that with a guy like SJax who isn't in an ideal situation but is insanely talented. It's a tradeoff in a redraft, you weigh one equally with the other.
Keeper - Keeper leagues vary so much due to how the keepers are decided and which draft picks you get, etc, so I don't bother
Dynasty - absolute minimum of 3 years of production. Unless he can pretty much wrap up an overall win for me in 2008, I'm not going to rank him highly if I don't think he has 3 good seasons left. I give points to someone who is young and obviously talented but who is not in a great situation (i.e. Lee Evans, Calvin Johnson, Dwayne Bowe) as I take talent over situation in most cases. Someone like Fitz, however, who is immensely talented, is stuck in a bad situation with a QB that I think will not be able to get the ball to Fitz often enough, and he is stuck for 4 years with that QB (unless they come to their senses and toss Leinart to the curb). I still think he is a high-ranked dynasty guy, but I would be forced to drop him beneath someone with less talent in a better situation, simply because Fitz is stuck and will be stuck for several more years.
Again, the key for dynasty is AT LEAST 3 years production, or a title in 2008.