My B-I-L is a rancher. They keep one calf a year, primarily grass fed, to butcher for themselves. I've eaten a fair amount of it, and I must admit, its not too good. A bit tough. Not as rich and flavorful as grain feed. Similar thing with a cousin who raises a few cows. I'm not saying its bad, its just not great and not near as good as good store bought and does not hold a candle to prime beef...which I get almost never.
I've done a fair amount of reading about grass fed beef and the truth is, there aren't many really good reviews. But there are some. The reviews are better if you read ones done by people who have an idealogical investment in the whole organic/natural movement.
Which just shows that it is a matter of taste. Traditionally beef has been valued for its fat content and fat flavor. I just don't think grass fed beef is ever going to be achieve grain fed fat and taste. But that does not have to mean that grain fed is better. It just means that it is different. But people's taste for beef is going to have to change for the grass fed to generate the same demand and willingness to pay top dollar that grain fed has.
The other thing that seems interesting is that in the reviews, the taste and quality of the grass fed beef varied a lot from farm to farm. I imagine types of grass, additional feed, levels of activity, etc all come into play.
I have never purchased commercially sold grass fed beef. But I like what most people like in beef, which is the fat content. Sure, its not as good for you, and it costs more, but man it tastes good. Like nothing else really. And I'm not averse to lean meat. I eat more venison than anything else. But when I really want steak, prime rib, etc., its going to take a lot of convincing for me to try grass fed, especially if it is expensive.
I do like the idea though. I've been trying to get my B-I-L to isolate about 1/4 of his herd to sell locally to people who want grass fed. I think he will need to feed some corn, but I would not give that part of the herd steroids...because the folks wanting grass fed usually don't want that. I think this would just provide a hedge against the beating that cattle ranchers take from the middlemen/buyers.