Carbonation take place with only temperature and pressure, and will equalize given time (24-48 hrs). Add mechanical energy, such as shaking, and you can force carbonate in minutes. I will chill a 5 gallon corny keg down over night (actually its already cold crashed in the fermenter before xfer), Hook up CO2 at about 30 psi, and rock it on its side, back and forth 75- 100 times. Depending on your agressiveness, style guidlines and such, it may be more or less. Equalization is usually around 12 psi of head pressure for 2.5ish volumes. This is great for small bars and home brewers, because small keggerator setups require 3-6 feet of beer line to get to the tap, which just so happens to reduce the pressure in the line at the tap to give the proper pour. A longer run of line (10, 15, 20 feet) would require much higher head pressure in the keg to pour out the tap at the right pressure, and if you use CO2, it will eventually overcarbonate in a matter of days. To get around this, bars use nitrogen (which does not (kind of) dissolve into solution, or they use a beer pump. To use two kegs with one CO2 line, you must use a splitter. If you have a old ale (1.5ish volumes) and a hef (3ish), you will need dual regulators. But most people cant tell the difference anyway.