Sorry about my ignorance but, what pool already have merged mining?!
Slush, BTCGuild, Eligius, NMCBit, SimpleCoin.
Of the big 5 only Arsbitcoin and deepbit don't currently offer merged mining. Arsbitcoin has indicated they may offer merged mining but needs to work through some issues. There is a lot of noise on deepbit thread on why it hasn't offered merged mining yet so either deepbit offers merged mining (easily doubles NMC hashrate) or expect DeepBit to be getting smaller in the future.
I would be very surprised if all of the top 10 pools don't all offer merged mining within a couple weeks. Too much "free coin".
I mean if you could earn x BTC per week or 1.3x BTC per week for the exact same miner, hardware, electrical cost, and end user "work" which would you pick?
Do you know if the http://mining.mainframe.nl/ pool offers merged mining?!
Thanks!
Thiago