If something is very juicy, you will have juice sucking out, especially when people cut the bags just a tad too short in an effort to save money. One way around this is to freeze first, then vacuum seal. Berries, for example, especially fragile ones like raspberries need to be quick-frozen by putting them in a single layer on a cookie sheet. Then measure into portions, vacuum seal, and put back in the freezer.
One thing to think of. If you're doing 30-Day Gourmet or similar OAMC marathons, I would not bother with a vacuum sealer and instead spend the money on good square/rectangular freezer containers--reason being that you are in theory turning these meals around quickly. Save the bags for true long-term freezer storage.
Don't bother with the cheap bags--remember, as you move things around in the freezer, or drop them 8(, the bags have to be able to withstand such treatment. Boxes in the freezer have sharp corners that can and do slice bags, and you won't find out until you defrost the item.