I've had a Dell QuietKey in the closet for a little over a year, it was given to me by someone who found it at work and said it 'felt mechanical.'
I cleaned it up last week, and outside of the yellowing of the ABS plastic keys I have to say for a rubber dome keyboard it is pretty great.
They have a great tactile feel, which, after the switch breaks through the bump, goes down to bottoming out very smoothly without feeling mushy.