Absolutely. But that's the worker's responsibility, not the requester's. I was thinking in terms of the requesters saving themselves a bit of money by not doing paperwork. They don't have to send you a 1099 if your earnings are less than $600, so as bootybitch remarked, they can pull a qual/soft block when you get close to keep from doing it. Although these days you'd think it would only cost a few cents each to generate a 1099. Then again, if you had to do it for a few hundred Turkers, I suppose the administrative overhead, postage, and so on could add up.