Hey Nervus (I love your username), if you already know all of this, apologies.
Bitterness in beer is measured in IBUs (International Bittering Units). If you are looking to make a lighter beer that may appeal to BMC drinkers, IBUs in the +/- 15 range is about right. You can see the hops schedule I use in a lighter beer, with a bitterness of 14.3 IBU here http://www.singingboysbrewing.com/Dr...-t-a-word.html
Hops have an alpha acid rating, sometimes shorthanded as AA%. The higher the percentage, the more bitterness (IBUs) the hops will add to the beer. If you look at the recipe link above, you'll see that I used two types of hops, one 7.4% AA and the other 5.2% AA - these would be considered lower bitterness hops.
Another factor is the length of time you boil the hops - the longer the boil the more bitterness is extracted and the higher the final IBUs in your beer. One hour, as described in your recipe, is a standard length for a bitterness hop addition. Sometimes, we add hops at other, short times, too to impart some bitterness, but also flavor and aroma.
You can predict the IBUs you will get from a recipe, using either long-hand math (there are some guys here who really love doing that) or using some software like BeerSmith.
Cheers, Salud and Skoal!