Since Hubski works by following and sharing, you can submit pretty much as you like. You might get some folk choosing to ignore your posts if it's too high frequency, but you might get some followers who love it. Personally, I'd start at one napkin per day. :)

Thanks, glad you like it here. I can't speak for "Hubski" but I can say that I really like the napkins and if Hubski has been set up properly people should be able to avoid the flood if they wish to. I imagine that you have interests outside of the napkin art too, I might suggest mixing it up a bit with your posts if you're worried about too much of one thing. Either way, glad to have you here and I look forward to seeing more of your work.