1.5 to 2 inches of head is perfect. In most foreign countries they pour 3 inches of head and “cut” to release the bubbles. You may see this a lot on Three Sheets. They us “foam scrapers” like this:
http://tiny.cc/Scraper The foam releases the yeast into the beer and allows some of the carbon dioxide to escape before you drink the beer. (all info taken from BeerAdvocate.com and AllAboutBeer.com)
11pm