I guess I've got to come down squarely in the middle on this one...
On the one hand, I can't stand truly "affected" performances that are just so obviously a put-on. Two examples from the "Celtic Woman" show come to mind (and I know I've bitched about this before, so apologies). One--the fidder chick in her pretty sparkly dress bouncing around like a bobblehead doll when she's playing "The Butterfly" slower than even I could dance to. Her movements are SO exaggerated compared to what she is playing that it just makes me cringe. The other example really burns me up, which is having the "folk harper" on stage playing "Ave Maria" without flipping a single lever, which is not technically possible--clearly the pedal harp is in the orchestra playing and the girl onstage is playing sparkly arpeggios and smiling beatifically. As a harper myself, the obvious sham sort of offends me.
On the other hand, a bit of showmanship doesn't bother me when I really like and respect the performer. We've had a few amazing musicians play at Dusty Strings, and a few examples also come to mind: James Hill, ukulele madman, the biggest show-off ever--and yet as he plays his lightning licks he's grinning at the audience as if to say, "I sure hope you're having as much fun as I am!" He's clearly welcoming the audience to share his glee, rather than holding himself above them.
The other awesome example is another harpist, Park Stickney, who came to our Harp Symposium last year and will be back this year! For the concert we got him both a pedal and a lever harp, and at one point he was playing "Take Five" on the pedal harp with one hand and casually reached over, grabbed the lever harp with his free hand, tilted it to his other shoulder and started playing it at the same time (obviously a simplified accompaniment). Again, ridiculous showmanship, but there was no sense of "superiority"...he knew he was playing for a bunch of harpists who could appreciate and enjoy just how complicated it was, and it was like a gift he was giving us, rather than a stuffy self-important thing. He had that same gleeful expression as James Hill (if we ever get those two on stage together there may be some sort of rift in the space-time continuiniuiuinuum!)
Ack...I blather as usual. But there's my two bits.