David gets the prize on this one, I didn't even think about that, but he is absolutly right.

1) They don't. Until they are opened. Fluid dynamics and answer #2
2) Nucleation sites

Unless the interface area is protected by a non-volatile solid/liquid

Pete,

Must you complicate everything?
The whole point is to apply "pressure" so you consolodate the laminate and remove excess resin. Vacuum is a conveinient way to get about 14lb/in. You can get 80-90 out of cheep home compressor if you can manage to build a vessel to hold it. A pressure chamber is a lot more complicated than tacky tape and plastic film, but it is possible to achieve the same net effect.
Rollers and sqeegees work to some extent with open molding, but if there any loft to your fiber pack it is extremely difficult to get a good fiber to resin ratio.

Yes, but you just end up with a really crappy 1 stroke piston pump

Look at a Manometer. Fill a tube taller than 33 ft with water. Upend the tube of water into a container of water. The column of water will drop until it is supported by the air pressure (~33 ft). The pressure in the void in the top of the tube will be the vapor pressure of water (~0.5 psi). If you use an IV bag and a flexible tube, start with the tube full of water, the open end in the container of water and then just hoist the bag up a tree.

Lets assume you are going to use this thing to pull a vacuum. Assume 1 ft of that tube has the same volume as what you are trying to pull a vacuum on. If you make your tube 43 ft high the best vacuum you can pull will be 14.7/11 +0.5(Vapor pressure of water). There are loses and other factors but I don't remember what they are.

I actually saw someone try this once as a college project. They were able to pull a couple of psi of vacuum. They then showed a hand powered lab vacuum pump beat the hell out it.

A better system is a vacuum oil changer. I have a metal one leftover from my big boat days but it works like this

http://www.liquivac.com/buyonline

I can get about a negative 7-8 psi per the gauge, if I work really hard and when I finish with, I can change the oil in my lawnmower

the nice thing about the vacuum, though, is that it tends to expand, burst, and evacuate bubbles in the resin of the layup. Applying just external pressure would compress those bubbles and they would remain in place.

True, but the nice thing about large differentials in pressure (this includes the difference between atmospheric pressure and the applied vacuum, or atmospheric and the applied pressure) is that as long as the material is flowing, the air will rush to the flow front. In production comression molding uses this to get void free laminates. Puddle the resin in the center and as you apply pressure the resin flows out and takes the air with it. Air voids (short circuits)under vacuum will not "move" either without flow.

So which is the superior method for home building dagger boards, rudders and other relatively "flat" panels, vacuum or pressure?

For pressure I'm assuming you could put the part between two flat plates and pile weight on it. No? Yes?

Inquiring minds...

And I got this in the "mail" this morning. Anyone know anything about it? http://www.jamestowndistributors.com/userportal/main.do?&campaign=email060512

you could park a car on it...but, lets say you had a mild level of vacuum at 20 inches of mercury (-9.8psi) on a daggerboard that measures 60 inches by 10 inches, you will need to park 5,880 lbs on it and somehow get that pressure evenly distributed on the layup.

Ah, enlightenment...