Hmm, again, from that wiki page:
Including in Blocks
This section describes how the reference implementation selects which transactions to put into new blocks, with default settings. All of the settings may be changed if a miner wants to create larger or smaller blocks containing more or fewer free transactions.
30,000 bytes in the block are set aside for the highest-priority transactions, regardless of transaction fee. Transactions are added highest-priority-first to this section of the block.
Then transactions that pay a fee of at least 0.0001 BTC/kb are added to the block, highest-fee transactions first, until the block is not more than 300,000 bytes big.
The remaining transactions remain in the miner's "memory pool", and may be included in later blocks if their priority or fee is large enough.
I know, that is talking about the reference client's block construction behavior but it might explain a few things if it is a fair representation of what miners are doing.
A quick scan of my mempool of unconfirmed transactions and their priority, sorted by "highest priority":
22247 29510957894.26107407
22251 24617855466.11368179
22237 23797564629.60096359
22245 23794448299.07243729
27302 21127378315.33507919
22238 21059217907.33554459
22229 18540419334.94335556
22254 16502444715.59822273
22237 16130040247.36238289
22251 15074281814.33272171
22249 15068602923.64821625
22240 12768199194.55590630
5965 10029852114.08262253
7176 8947361947.19983292
2852 7769685225.87504864
22240 7673617191.58819962
4332 7591994500.56230640
5693 7554179627.29180527
22241 7394041900.16759014
9256 7123151255.12517929
5559 6836646125.44707775
259 6533343333.33333302
6436 6173324479.56040573
523 6033913454.75903320
1261 5822628219.26124096
16646 5444277224.78949356
258 5092818188.14678001
....
First column is bytes. That's pretty much going to eat up the "30000 is reserved for highest priority" for quite some time. You're currently ranked #171 from the top of that list. There's 577781 bytes of "high priority" traffic ahead of yours.
Because your tx is fee free, it won't fit in the second group.
It is unclear how many pools use the transaction selection models that the reference client uses, or what quirks they have.
This is going to take a while. Be extremely careful if you're thinking of resending, it could still confirm.