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As for the square (air bleed) zip locks.  They are heavier than even the heavy duty zip locks and the nylon is a bit slicker.  The downsize for travel is that when placed on a flat surface (like a bed) they tend to slide all over the place rather remaining stacked.  After a while, I was afraid that a bag might slide off the flat surface into a cranny and be left behind.  So, I've mostly ditched using them for luggage-based travel.

I'm real attentive to where I lay my gear. It's either under my Dri-Fly or inside tent, but I could see how what your saying could happen if your prone to scattering your gear all over camp :o
Last trip I bought a mesh style small duffel and laid the bags in them. Worked great but you still have to put things where they belong ;)

zski,
I found that if you make sure the zipper is secure before rolling, they stay sealed until you open them.
I took a plane trip to AZ from MI a few years back. Used my tripping bags to compress clothes so they fit in my carry-on. I would of thought if they were going to leak they would of done it then.
One " drawback" if you use them while traveling on a plane is that you can get so much more in your suitcase, you might find yourself over the weight limit ;D