I thought my new refractometer was the cat's ass when I first started using it. For all the reasons that ajf points out, I loved using it.
Then one day, I tested a sample of unfermented wort with my refractometer and my hydrometer simultaneously. I discovered that while hydrometers measure liquid density (all dissolved sugars), refractometers aren't all created equal in what kinds of sugar they measure. My observed gravities differed by ~12 points for the same sample on the different instruments. It turns out you can compensate for this, but needing to go back to beersmith or some other electronic device in order to calculate what the observed refractometer value really means turned me off on the whole idea.
Refractometers are still cool, but when yours doesn't measure maltose accurately and needs a computer to calculate correct readings...yea, I will stick with my hydrometer and deal with it.