This is: https://github.com/bitcoin/bitcoin/issues#issue/86
currently (2011/03/01) a backlog of transactions that dont seem make it into blocks is building up (according to ArtForz now 670 transactions).
People are starting to complain, see http://bitcointalk.org/index.php?topic=3835.msg57031#msg57031 for an example.
This was discussed on #bitcoin-dev
ArtForz> that tx should have a score of 20567855
ArtForz> so it falls short of the dPriority > COIN * 144 / 250 test
ArtForz> and as tx size is > 4000, fAllowFree is never true for it
theymos> Ah. So it will never confirm?
ArtForz> probably not
ArtForz> looks like the tx-sending code needs some fixing
molecular> like not generate a tx with a score too low, or suggest to add a fee?
ArtForz> yep
ArtForz> check size and priority of transaction, if it's > 4kB and score < 57600000 require min fee
ArtForz> maybe reduce the size limit to 3.5k or so, otherwise it can only get into an otherwise empty block
Maybe the transaction cache should not be unlimited?