But flash mining isn't really flash mining!  Some accounts above me have up to 450BTC outstanding.  Even assuming spare hashrate was 30 THash/s (which it isn't) and that difficulty remains constant (which it wont), this 30 THash/s will produce approx 3.5 BTC per day.  Therefore to flash mine 1 single account (this may be a big one, but there are bigger ones I know of), it will still take 128 days plus!

I suggest that any spare or bonus hashrate is distributed evenly over all existing (or old) accounts, in direct proportion to the amount of BTC you have remaining.  This should be easy to implement and manage and should be straightforward to re calibrate when an account gets completed (everyone gets a fraction more power).  I consider myself pretty early into this, but limiting any bonus to a few accounts means that all but the very very first people to invest will see anything back.

And please dont change the bonus structure for any existing accounts (and preferably not for the queued amounts).  We all signed up for the current T&C.  Any new rules, whatever you decide, should only be implemented for deposits made after the rules are published.