So how much is a coffee?
My only experience in Europe was flying through Madrid Airport (on the way to Morocco.)
It was a triple combo... the dollar is fairly weak, airports always make stuff expensive, and Starbucks is pricey as well.
I got a large coffee (admittedly not black, it had some stuff mixed in....) and it was like 8 euros, this was $12 or so. Ouch!
Here in the midwestern US, cheap diner or fast foot coffee is like $0.75 to $1 or so (often this is quite burnt and nasty), regular coffee about $1.50, some really frilly thing could get you up to $3 or $4.
On the other hand in Morocco, a nice little shot of coffee was like about 5 dirhams (back then this was about $0.71). It is a small shot of very thick coffee, very well roasted and tasty and really has a kick to it (it seemed pretty similar everywhere I had it). The natives LOVE sugar and add as much as physically possible; I thought it was great black, but inevitably after a sip or two someone would say "no no you surely need some sugar" and I'd put it in, this was good as well 8-)
Oh.. back to the point... this makes a big diff on how big a deal a 10% discount is. Saving 7 cents a coffee is not worth it too me, but saving like a dollar apiece could be.