If the curve is altered to the one Taraz mentioned yesterday, the bigger the potential payout, the more impact a flag will have, and so even a small account could have an impact on a large payout. I have no idea with regards to the math though.
There is discussion of cheaper flags, so maybe a couple of free ones each day that don't reduce VP - again, I've seen nothing concrete and just passing on rumors.
The flag would reduce the payout, and so author, curators, beneficiaries etc would all lose a %.
I think the best time to disagree would be when the post had topped out rewards-wise.
This is what I understand and it could all be a load of tosh :)