It seems that very few people actually use them, and on this board in particular, it is rare. Most people either wait till the fish has been in the store awhile or trust their "source". Certain reef fish don't fare well in a q-tank type setup.
A hospital tank OTOH is indispensible IMO, I buy aggressive fish (cuz' I'm such a tough guy

) and sometimes personalities don't mix well or a fish gets stressed or something and I need to have an alternate residence ready if that happens, hopefully I'll find a good 'balance' soon. Also for outbreaks of disease on a fish where treating the main tank is impossible a hospital tank will be handy (if the fish are catchable).
I use the emperor series of powerfilters on two tanks (and an eclipse hood on my 10g) - so if I need a true hospital tank I'll remove the bio-wheel from the main tank to the q-tank and fill it with water from one of the main tanks - voila, instant setup. Others keep
sponge filters in their sump/sandbed then switch them into the q-tank when they need to use it.
Hope I made sense
