This particular topic has been already been discussed several times. Last time was only a few days ago. The best theory right now is that it's server dependant (which I think we have one confirmation for) with the uswest/middlecoin.com server currently having the lowest profits. If that's the server you're using, try using one of the beta servers that are closest to you.
Since the 14th I've had two payments that have never been received. I've checked with the exchange that my address leads to and they have no deposit issues and no record of my btc coming in. I'm hoping its just a mixup in the database but 2 days is a long time to wait for btc. Pool operator I can give you the transaction addresses if you PM me.
He's probably not reading this thread anymore. PM him instead.