Excellent post, Laurabeth.
I just wanted to clarify or expound upon the information contained in the quote above.
Most silicones are not ionic at all, and they are attracted to the hair due to their overall hydrophobicity (water-hating) tendencies. Surfactants, by nature, all have a hydrophobic portion, and like attracts like. Therefore even non-ionic surfactants can and will attract oils (which are hydrophobic) away from the hair. This is how they are meant to work and how they do indeed work. This is the basis for oil-in-water detergency, where oils are emulsified by being absorbed into the center of a micelle, which is solvated in water by the surrounding shell of hydrophilic head groups. (The hydrophobic effect, micelle theory, and all of that is a part of colloid chemistry, which is based upon some very fundamental principles of thermodynamics, which maybe we should go over some time for everyone.)
The limitation upon many commonly used nonionic surfactants is that they have a larger hydrophilic (water-loving) head group. These bulky head groups are repelled from one another due to a phenomenon known as "steric hindrance" (basically - things all need to occupy their own space, and the larger things are - the more space they need). This impacts the geometry of the micelle that is formed, making it less able to hold as much oil in the interior (one can do more research on this by looking up "the priniciple of opposing forces"). For this reason, these surfactants are less efficient. They can have a similar effectiveness as ionic surfactants, but that would require them being used in larger quantities. Most often, the two types are mixed in formulations, because together they enhance one another's capabilities in micelle formation and detergency.
So in summary, the ability of a surfactant to remove hydrophobic materials from our hair is more closely correlated to the size of its polar head group than to the nature of its ionic charge.
I wish I had a chalk board here, because I feel that colloid and surace science are so much easier to teach when I can draw pictures.