Quote from: bitcoinandroid on October 19, 2011, 05:31:13 AM

One more I was just thinking about: when selecting coins to create a new transaction, does it make sense to use transactions which are not yet in a block?

Only if you're sure that the transaction you're spending will eventually be included in a block. Bitcoin spends 0-confirmation transactions that it has created, but never 0-conf transactions from other people.

These transactions will have very low (maybe 0) priority, but this will increase as the inputs age.

Quote from: bitcoinandroid

Similarly, does the official client clear out orphan transactions after some period if they haven't made it into a block?

No, but that would be nice.