The construction of a 3 layer laminate is actually quite simple. You have the outer layer which gives the pretty color to the jacket. The middle layer is the waterproof membrane be it eVent, Gore-Tex or any other proprietary brand. The inner layer is there to protect the waterproof membrane, which is quite fragile, from abrasion against your undergarments.

There are 2 things that make a jacket 'waterproof': DWR (durable water repellant) coating and the waterproof membrane. The DWR is applied to the outer layer of the 3 layer jacket. When water hits the outer layer, the water will bead up and roll off the jacket. If water gets passed the DWR coating, then the waterproof membrane will keep the water from going through the jacket. Eventually the DWR coating will wear off at high abrasion points of the jacket. When this happens, just put your jacket in the dryer for a quick 15 minute tumble at medium heat. This should renew your DWR coating. Eventually you'll need to reapply a new DWR coating which you can buy at any outdoor retailer; brands like Nikwax or Grangers are great for renewing the DWR on your jacket. Keep in mind that dirt and sweat can also affect the DWR coating on your jacket.

The reason why DWR is important is because once the DWR wears off and the outer layer starts to wet out (absorb water) then the breathe-ability of the middle layer goes away. At that point, you may as well be wearing a garbage bag over your body keeping rain out but still getting drenched in sweat.

Waterproof membranes are not magic. They will not let water drops through the jacket, but will let some water vapor through. With that being said, you'll be wet from sweat but not from rain, but less sweat than wearing a garbage bag.

Comparing eVent to Gore-Tex, Gore-Tex is more wind proof but eVent is more breathe-able. There are videos on youtube that show the breath-ability comparison between the 2 membranes. Personally, I am a huge fan of eVent, and I plan to purchase an Elite 2.1 when my pennies are saved up.