Mtgox doesn't pay fees for the sweeps or wait until there is an adequate balance, they send transactions out that have little hope of block inclusion if you send the address a stream of satoshis.
Thanks.Is there any service or application or method to auto-sweep funds with top priority as soon as they arrive? If not, how difficult would it be to build such an application?
Maybe I'll ask etotheipi if he wants to include it in Armory.
We could add the ability to have a fee added, but it means that you could end spending bitcoins without warning, which is a bad idea.
For information, sweep happens as soon as we see a non confirmed transaction for your bitcoin address.