We keep it to around 25-30. We send to close friends, parents, grandparents, and just the aunts and uncles we are closest to and speak to beyond just holiday get-togethers. We also send out a few random ones (one to our dog behaviorist, one to our vet, etc.)
I ordered 35 and definitely had my head up my ass. I had to order 25 more because it wasn't enough 60 is definitely enough with some left over for the scrapbook.
I ordered 70 cards because I had a bunch of deals and coupons, but we normally send out 40-50 cards. I don't think we'll have a problem adding some more people to our list, between DH's co-workers and a few friends of mine.
Every damn year I make (shut up, I still am the schmuck that hand makes cards) like 50 and run out, as if like magic. Then I have to run to the nearest store and buy some remedial cards, shove a pic on it, but at least it's something right?
This year I ordered 75. So naturally I'll send none and have a shitton left over, I surmise.