You know, at the average gig, it doesn't bother me, and there are times
when it's even perfectly appropriate -- a similar mass sing of "Four
Seasons In One Day" happened in Boston during the ONE NIL tour a couple
years ago, and you can usually count on audience singing at a Polyphonic
Spree show -- but it's the context that counts.  Club shows in Boston are
traditionally miked at a volume just slightly under permanent nerve damage,
and someone would have to be singing in my ear with a megaphone before I
would hear them over the soundboard.  So go ahead, sing all you want.  But
house concerts, which I attend regularly because of my wife's family and
their standing in the local folk scene, are another matter entirely.  About
a year ago, I was seeing Les Barker, a Scottish singer and poet, in a
backyard concert/picnic out in the burbs, and I was stuck behind this one
woman who was not only singing along to the songs, but RECITING HIS POEMS
ALONG WITH HIM!  

I eventually took to spitting my watermelon seeds into her hair, so I did
get some enjoyment out of the evening.  But still.

S