If you place a market order then yes it will execute at the best available bid in 45+ minutes which could be 50 or 150.

So you have a couple options:
a) FOR THE LOVE OF SATOSHI .... STOP USING MTGOX.
b) Don't place orders when the lag is more than a few seconds.
c) Use limit orders to ensure your order executes only at the price you want or better.