From what I have read, it seems most people like them, but I know a couple of guys who installed them on existing doors and had nothing but problems. I suspect it was due to the torsion springs not being adjusted properly which was causing some binding or uneven lifting of the door... but hard to say for certain.
In one case the guy had the installer come back out and replace the openers (same issues on both doors). One door went through three openers, the other required two, but eventually he seemed to get the kinks worked out. Not sure if this required any adjustment to the doors or springs.
In the other case I knew of, the guy ended up sending them back and going with a conventional opener. He was of the opinion the technology wasn't quite up to speed yet.
Aside from these two, I don't know anyone personally who has them. I go through the local Parade of Homes twice each year and the garage is one room I always check out... I think in the 100 new homes I've viewed in the past 5-6 years I've seen one with shaft mounted openers, and that was in a case where the guy had two drive-on lifts so he could store four cars in two stalls.
One thing to be aware of is you need to ensure you get electrical power to where the opener will be located. This isn't typically a problem, but something to be aware of if you happen to have a tuck-under garage as it may require some conduit or other surface mounted options.