Everyone should do it once.
One day is enough.
I took a bus from Berlin to Munich for the first weekend of Oktoberfest, which actually started September 21st. The night before, I met a vampire from Romania who bedazzled us with card tricks. Dawned in my dirndl, I awoke bright and early to catch the train into the festival, where we waited in a crowd outside the Armbrustschützenzelt tent for a bit before being one of the first waves allowed in. We secured a few tables and waited til noon.
My first liter of beer came right out of the first-tapped barrel of Oktoberfest 2013. The rest is history.
A word of wisdom: EAT. Eat as much as you can, so you may continue to drink coherently. ;]