It's not really a problem as much as it is people buying shares on pools that can't handle the load which we are still fine turning to protect our miners. Updates coming soon will address this and make buyers pay for rejects on pools that have issues so the miners are not penalized for it.
EDIT: We get a lot of pools ops testing their system which is not something miners should have to pay for with rejects and stales.
Over a very extensive sample, I have a .78% reject rate. GPUMAX's tends to be MUCH higher when doing leased work, hard to figure without the figures being broken out, but my current rate is 1,674,816 accepted, 79,673 rejected, or 79,673 / 1,754,489 ~ 4.54%, and I think the bulk of that comes from the public work. I would gladly accept not being paid for up to 1% rejects, but I think anything above that ought to be paid for by the buyer.