My first attempt resulted in a 3db gain.
My second increased almost 9db.
A friend has a few acres of land and has a barn/building in about 180ft from the home. We put the router antenna in the window of the home facing the barn, and the barn antenna in a front window.
We had great throughput and very little losses.
Aiming the cans a little better would have increased the throughput, and FOLLOWING THE directions and research DID increase cantenna results.
Length, diameter, and material all matter. Take a few minutes at the grocery store with a ruler or calipers to find the best can for the job.
My results were average for what the fellas on the linked page got. So if you follow the directions, you can easily have a great $5 antenna.