Although I haven't ever used quality honey in my meads, and I doubt that I have ever tasted quality honey, I would say it is very important. Very, very, very.
If you consider what goes into mead step by step, you'll notice something. This is a very simplified list.
1) Nectar collection - what floral source?
2) Bees make honey
3) Honey collected, processed minimally
4) Honey + water + yeast
5) Lots of time
6) Yummy mead, drink up.
See how far apart tasting and nectar collection are? If the floral source for the honey can be specified through the taste of the finished product, then I think the answer to the poll should be very obvious.
Edit:
I would also like to add that I have made meads in the past with extremely low quality honey, so low that the floral source wasn't even mentioned on the label. The cyser turned out okay, but almost no honey flavor could be tasted when the mead was chilled. Once it warmed, I had to take a big drink to get a hint of honey in the aftertaste.