Risk of sending transaction with lower fees.

[Kazuldur]

Is sending big transactions (~13KB in size) with low fees like 0.0005 BTC safe? I'm maintaining one of the BTC Faucets and even using sendmany fees are quite expensive. There are transactions, that have done that (thanks camda for that links!):
http://blockchain.info/tx/cac7d4b01d07172492fb4fffe9e6ee15cab130b74cab356581be501505ef139e
http://blockchain.info/tx/f0bff77372aa7c003608953a64ba792c52ce92493c30486b8b0bc1a4c54629ae
http://blockchain.info/tx/9079365f0b966be73a9cbd81509491a2da89fcb65be2d5aed7f0114fbd9aab7e
http://blockchain.info/tx/06c0afcf8e978ee0b598f9b3ff17d4c9d3a6f1e4d097a00a70d1f400bf1f0d83

Is there a possibility that such transactions won't confirm at all or only after a few days? Is rebroadcasting needed? If so how often should I do that?

[DeathAndTaxes]

Your client will continually auto-rebroadcast until the tx is included in a block so there is nothing "special" you need to do.

In theory it could be excluded by all miners and never be included in a block but as a practical reality the worst that will happen is the transaction is delayed.  It could be delayed significantly though (hours or even days).

BTW many pools consider ultra low fees the same as free tx.  So your tx gets lumped in with the other giant, "spammy", low priority, freeloader txs. In other words not much rush to get to them.

[zeb00]

It is an interesting question
the answer lies in how the major pools are accepting transactions at the current time (as they solve a majority of the blocks)
does anyone know which pool are requiring minimum transaction fees to include a transaction in there blocks currently?
what about the official bitcoind when it is used to create blocks for solo mining does it prioritise/exclude transaction added based on fees?

EDIT DeathAndTaxes beat me to it with most of the answer to my questions

[pieppiep]

On the deepbit site under help :

Deepbit's transaction fee policy
(This is not related to the pool's payments to our users)
We think that free transactions are very important for the Bitcoin system so we are including as much free transactions as possible into our blocks, possibly more than anyone else. But sometimes a fee may be useful, so here is our fee policy:
A transaction is considered to be 'free' if the offered fee is less than 0.01 BTC. Free transactions are only accepted if they are less than 2000 bytes in size and have no more than 5 outputs. Outputs less than 0.01 BTC are not allowed in free transactions. The minimum fee for non-free transaction is 0.01 BTC for each started 1000 bytes.