Also having trouble with MyBitcoin...
Transfer was confirmed on their website, but no trace in block explorer. Even stranger is that the incoming transfer from another mybitcoin user with which I funded the outgoing transfer is not present in block explorer either! It seems I never had the money I never received.
Now the mybitcoin site is down and I'm wondering if I will ever see that currency again.
Maybe (hopefully) they took the site down after noticing these problems and the outstanding transfers will be initiated when (if) it comes back online.
This is a huge headache.