One of the problems with a high ammonia concentration is that the wrong bacteria will develop. As the concentration starts to drop, the bacteria we have established don't get enough ammonia any more and you will not have established the right bacteria. The shift from the bacteria we want to the ones we don't want happens somewhere around 8 ppm so you will want to keep your concentration around the 4 to 5 ppm level while trying to get your cycle going.
Jonnythan, a 5 gallon will likely take much less than a teaspoon, I don't remember exactly. You can probably smell the ammonia if you have that much in it.
I just did a quick calculation and it should take slightly less than 1/4 teaspoon in a real volume of 5 gallons to get to 5 ppm. Many 5 gallon tanks don't actually hold that much water so you want even less ammonia than that. Warning, when I calculate my ammonia for a cycle, the first thing I do is add half that much, test and adjust based on my readings. There are just too many variables to do it by adding everything at once.