TheBigNinja,
Technically speaking the weight of the rider isn't actually relevant when it comes to what the sag should be. The idea of the static sag of your suspension is to have the bike's chassis sitting at a certain point along the suspension travel so that as you go over bumps, take corners, etc the bike doesn't bottom out or top out (is that even a phrase? but its still relevant, you don't want to hit the top of your suspension).
So, why doesn't the rider weight matter? Since the static sag target is a point along the suspension travel it will be the same point for a 300 pound rider as a 150 pound rider what will change is the preload and spring stiffness required to obtain this target.
The general rule of thumb for most street bikes is between 25mm and 30mm of static sag (although I've seen some people suggest as high as 40mm), typically this should be the SAME both front and rear however I've also seen some people suggest more sag in the front than the rear. The reason that some would suggest different measurements is because ideally the static sag isn't a specific measurement for all bikes, but actually a percentage of the total suspension travel. I just don't remember what that percentage is (I think its something like 60% of total travel and lets assume this is correct for the sake of the conversation).
So what this means is, if you have a dirt bike with a TON of suspension travel (100mm front, 70mm rear lets say) than the ideal static sag would be 60mm front, 42mm rear. A street bike might have 50mm front and 45mm rear suspension travel, which would mean the ideal static sag would be 30mm front, 27mm rear. These are just made up numbers but in my example the street bike's static sag are pretty close so that could explain the discrepancy between setting the front and rear the same or differently.
Also, the other main point is you actually want the bike to sit "level" that is, when the suspension is loaded and when the suspension is working it should be working evenly. In my previous post I described feeling like I was being ejected from my seat when going over a bump, that's because the front and rear weren't working evenly yet.
In the ideal world you would determine what the total suspension travel of both your front and rear suspension is and set each to 25-33 percent of their total travel, actually I just did a quick search and found this article which suggests that and sounds about right.
http://racetech.com/articles/SuspensionAndSprings.htm
Okay... so what the hell does this all mean?
Got time on your hands and want the best possible setup? Figure out the total travel, times that by 25-33% and set your front & rear sag appropriately.
Feelin' lazy or like this is WAY too hard (its not really when you do it), set both the front and rear to 25-30mm.