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From the release notes of the Bitcoin version that introduced minimum transaction fees:
... note that we intend to replace the hard-coded fees with code that automatically calculates and suggests appropriate fees in the 0.9 release ...
Has Gavin expanded on the implementation of this automatic calculation?
Yes, this has actually been going on for a longer time, and it is expected to arrive in the next (0.10) release.
Citing Gavin:
Instead of using hard-coded rules for what fees to pay, the code observes how long transactions are taking to confirm and then uses that data to estimate the right fee to pay so the transaction confirms quickly– or decides that the transaction has a high enough priority to be sent for free but still confirm quickly.
In practice, you'll be able to select the priority of your outgoing transaction and the fees will be calculated accordingly, taking the current "market situation" into consideration.
Once implemented, it will no longer be necessary to dictate or suggest the optimal fee centrally, as it is now.
You can read more in the original article by Gavin Andresen.
