From personal experience, I'd disagree with the statement that rooting hormones are ineffective, but it depends what you're using it for. I prefer the powder formulation to gels or liquids because there seems to be less chance of rot with the powder, and it has a longer shelf life, but essentially, rooting hormone preparations contain a chemical formula that, as far as the cutting is concerned, mimics auxin, the plant hormone largely responsible for root formation.
The use of root hormone preparations is neither essential nor preferable for many plants, but cuttings of many woody plants do seem to root better if they are dipped in hormone rooting powder, and also seem to produce more roots more quickly, reflected in more topgrowth at an earlier stage when compared with those rooted without hormone. In general, I'd use rooting powder for woody, semi ripe cuttings of shrubs, but not on soft cuttings, although there may be exceptions - I usually look up how to propagate a particular plant first from a reliable horticultural source, then decide on the type of cutting and whether hormone rooting powder is useful based on what information I find. I wouldn't use rooting hormone on things like perennials, or leaf cuttings and the like, and I'd say the more important factor in whether a cutting roots readily or not is related to whether it's the right type of cutting and whether it's taken at the right time of year.
Some information here regarding rooting hormones http://www.gardenfundamentals.com/rooting-hormones-what-are-they/
and how to use them here http://www.gardenfundamentals.com/use-rooting-hormone-correctly/
I've so far been unable to find any reference which states that, across the board, rooting hormones have been shown to be ineffective. That doesn't mean there isn't one somewhere, but I can't find it - they are certainly still in use by professional growers.