If your order is on their server why does it not execute? At mb i put on my orders, close the application and do something else and have never had 1 issue no matter how fast the market is on execution. I also never had unreasonable slippage. This is the reason why i endure mb's high swap rates because Oanda has really been getting bad reviews in the last year.
The only real issue i had with mb was when i was when they had no liquidity on usd/sek and i had to call in to get a price.
Oanda's platform seems to be a major issue costing traders money, maybe back in 2002 it was okay for brokers platforms to screw up but not in 2008, customers need to come together and send Oanda a petition to sort it out or you will all leave. They were very good in the past from what other traders say.