I'm wondering if combined mining is actually a waste of computational effort -
Bitminter has 11.5TH and got 17 BTC blocks today so far + 79 NMC blocks
Slush got just 9.7TH but got 25 BTC blocks today so far + 1 NMC block
So, if that's the case - I'd rather have BTC than MNC.
That's luck your demonstrating. There is no waste, all work goes to btc, and all work goes to nmc, if it's merged mining. You don't have some go to btc and some go to nmc, if the pool is merged mining, all work counts to all currencies. There is nothing lost.
Your stats just show good luck for slush, and bad (or at least worse) luck for bitminter.