A feature available through pull #1647 gives the recipient of a transaction a method to help get a transaction to confirm.
This feature is called "child pays for parent", and what it means is that the recipient of a transaction can create a new transaction using funds from the unconfirmed transaction, but any fee paid would help get both transactions confirmed.
A scenario where this is useful is where a merchant requires that a transaction have three or six confirmations before the item will be shipped out, but the payment the customer made ended up being a low-priority transaction due to it including many Bitcoin "dust" inputs. The merchant then creates a spend transaction using the funds received but pays a fee that will encourage miners to include both transactions.
Since this feature is not in the Bitcoin-Qt/bitcoind client, only miner pools that have a custom client that includes this pull will consider the fee paid by any child transactions when determining if a transaction should get included into a block.
Are there any miner pools or large solo miners who are running with this feature?