Artificial Gravity
The rotating cylinders do a good job of simulating gravity, but what problems arise from this? In fact, what reason is there for the artificial gravity, since the space stations seem to work weel enough with it. When people experience weightlessness, sometimes they suffer from nausea, dizziness, headaches, and vomiting, among other symptoms. Having artificial gravity would alleviate those symptoms, and on top of that, it would allow people to get used to an O'Neill Cylinder much quicker. However, the most important reason would have to do with the serious health effects. Muscles atrophy in a weightless environment, the skeleton can deteriorate, and the immune system can weaken.
Equation for Artificial Gravity
http://uplink.space.com/showflat.php?Cat=&Board=sciastro&Number=604347&page=1&view=collapsed&sb=5&o=0&fpart=
The equation above is for artificial gravity, and these are the parameters:
g = Decimal fraction of Earth gravity
R = Radius from center of rotation in meters
ƒÎ = 3.14159
rpm = revolutions per minute
The main problem with Artificial Gravity is the Coriolis Effect, which is where objects in a straight path are viewed as if they're in a rotating reference frame. This causes people to experience much the same symptoms as weightlessness, except that this is caused by the rotation of the cylinders. At 2 revolutions per minute, the Coriolis Effect does not effect people, and at 7 rpm few, if any people can remain unaffected.