I like the look of the glass, have you seen the bodum nudes (dual wall glass espresso cups, they even keep the heat in).  Just one thing to point out if you're talking espresso (rather than cappuchino) and you're looking to get it made, make sure that bottom is rounded and there are no corners around the bottom of the cup.  The curved bottom of the cup helps with crema production, if you've got a flat bottom and a corner where it joins the sides then you'll disipate crema as the shot pulls.  For example...

Got to say one of those, with a the glass insert and a good tiger striped shot on it would look superb.  I'm thinking...

Or one of the large ones with good latte art on the top like...

Anyway I digress.

I like the look of the cup.