I have a payout from Bitminter that is still unconfirmed after 17 hours.
And I have no explanation why my previous 4 payouts (1 per day) have confirmed in less than an hour, but this one is being treated different.
What changed?
The maximum size of each bitcoin block is limited to 1 megabyte. This is enforced by the client.
It's up to each miner (which means a pool operator or solo miner) to set their policy for what transactions get included in their blocks. They can even choose not to include any.
It could be that there are a lot of competing transactions that keep yours from getting picked up, or a lot of blocks are being mined by miners with more selfish policies that don't choose to include [m]any transactions.
Also the network hashrate seems to have stabilized now, so the network is about back to the intended 1 block per 10 minutes, rather than 1 per 7 minutes or so that we saw as the hashrate was climbing.
(This issue would be a lot less severe if we could somehow get rid of SatoshiDice, which spams the blockchain with tons of useless transactions.)