Well since people seem to have so many questions about ski size in addition to binding questions, here are some guidelines (Disclaimer: I am not the fore-most expert on this, but do feel I know what i am talking about. Knowledgable folks feel free to add):
Ski length has to do with two main things: 1) Skier weight 2) Skier Ability. Let's look at the first. Some people base how long their skis should be on their height. This is only because most people have the same body type, so it is okay to generalize. However, the flex and weight on the ski, and therefore how it performs is based on weight. So here goes:
If you are a lightweight skier , that is, 130 and below, you should probably be skiing something between 160 and 175 range. This is a large range, but that is because it is also highly dependent on skier ability. So, if you are new to freeride or skiing in general, I would recommend on the lower end of this range. If you have been skiing a while and are a "type III" skier, then I would say up to 175 will be fine for you. Some people can actually handle an even bigger ski, but if you are getting recommendations on your ski length, probably not the case for you.
If you are a middle weight skier , that is, between 130 and 160, your range can be anywhere from 165 to 180. Again, this is contingent on skill. Beginners, still to the lower end, 165-170 and better skiers can hit the upper end.
If you are a middle heavyweight skier , that is, 160 to 185 pounds, you will probably want a ski between 175 and 185, again based on skill.
Lastly, if you are heavy skier , that is, 185 lbs and up, as is my case, you will want something 180 cm or higher. Smaller skis will simply not perform like you want, and you will put too much force on the center and wont get the contact and control from the tips that you want.
As a final note: park specific and all around skis will definitely differ from big mountain and powder skis. Park and all mountain skis might stick to the shorter end of some ranges, while powder skis can go a bit longer. Also, know the flex of the ski you are considering. If it is an extremely soft flex ski, it might need to be a tidge longer than you would expect, and vice versa for stiff skis. We should make a table of the flex of different skis... whew, that is a good start I think.
I dream of winter.