I also experienced a near 80% rewards drop for block 237575.
Until Slush chimes in, we can only speculate that some sort of hardware error occurred during that window of time including blocks 237573 and 237574.
It's a shame to see BTC just vanish into oblivion.
Am also having big drop - almost 2 orders magnitude - for 237575. Average reward being .0045
Reward for 237575 being .000084421.
Similar situation blocks 237642 and 237540.
Work for 237574 gone disappeared.
Rewards on before and after sides of problem blocks seeming normal.
What happened is Slush must have adjusted it, but fixed it wrong not realizing 237574 was skipped.
when it got confirmed the Shares that mined 237574 were applied to block 237575 and since 237574 was a very short block we got a very low pay out on 237575. Before that adjustment my pay out for 237575 was too high but not high enough to make up for missing block 237574.
With block 237574 being completely skipped with no pay outs.