I haven't been around long enough to make clear judgements on how many keepers, but there are some thought here I agree with. The main one being, it depends on where you set your level! If by 'keeper' you mean publishable and would be accepted by a stock library, I think the threshold isn't too high - I've been on workshops with known photographers who will take well over a dozen 'keepers' in this sense, each workshop. Often more like a couple of dozen (although this includes different angles/formats of the same subject to sell in different ways). However, if you mean shots that really stand out each year, the shots that would find their way into your Best Of volume at some late point, these photographers generally believe 6-8 a year is a fair estimate.

I see so much rubbish in magazines, on websites etc, that I try to also maintain a high standard, which means I'm regularly throwing out shots that other workshop regulars like, and it's agonising to sort through shots when they come back from the lab.

This approach means you can be very hard on yourself, as well as on others - it's not unusual for me to flick through a David Muench book and think 'wouldn't have bothered printing that, or that' regularly - his volume of publishing seems to me to mean he needs a lower standard than some (although the 10 or thereabouts books by him on my shelves suggests I don't think he's that bad!); compare that with my impressions going through Burkett's book, or Dykinga's LF book, reading which I'm only occasionally saying 'I wouldn't have printed that'.

Still, I feel this harshness improves my output, as does reading more and more books.