the multiple posters for one show discussion, if i'm thinking of the same one as you steve, is here between these three posters:
50-100 sounds better to me too, although many of us just can't afford to give that many posters away; there's doing work for free and there's paying money for the priveledge of doing work for free, one is something we have to do sometimes, the other is something you should definitely approach with caution!
i'm not too sure, the two major shows i've done posters for have been collaborations and i haven't dealt with how many posters get sent to the venue. i think its a question of budget mainly, many of the artists on here contact the venue, offer a cool poster free of charge, print a run themselves using their own money and send maybe 40 or 50 to the venue (10-20 seems way too low i have to admit!) and try and make back the printing costs by selling the remainder of the posters; it may involve some dollars coming the way of the artist but that's gotta cover the printing costs, let alone the time and effort etc so i guess its a thin line we have to tread sometimes.
we had a similar discussion a few weeks ago about 2 posters for the same gig, if only i can remember the posters in question i could direct you to it,i'm not much help actually! i think this opened up another topic on artist's and payment..did the promoter let both artists know they weren't the only ones! were both artists actually paid etc, damn wish i could remember the posters, somebody else will i'm sure. :-)