I pick up bags of quarters sometimes at my last pickup of the week if I have enough cash to buy them. I don't expect much from them, but I do find occasional quarters. I had one bag earlier this year that had 10. I do find a number of Canadian quarters, but how many seems to depend on which bank I pick the bags up at. Certain machines seem to be much more likely to reject the non-silver canadian ones (probably just a better magnet). Although not a financial benefit, by searching quarters I also end up with additional foreign coin types that happen to be quarter sized. Lately, I have gotten a number of 50 Euro Cent coins this way (5 or 6, I think).
I usually figure somewhere around 1 per $2000 on average and slightly higher at some banks than others. At least one bank that I usually buy bags from seems to average 1 silver quarter per bag or so.
For example, around me I have absolutly terrible luck with dimes or quarters that come in the coin condoms (brinks) so I stopped picking them up a couple years ago when I switched to mainly bags.