120 with Bitcoin, 520 with PPCoin, etc.
Where is this info? I can't seem to find it on the wiki. Maybe it's in the source code? Anyway, that just means you need to wait a little bit less than a day to use newly mined bitcoins, or about 20 hours.
Here: https://en.bitcoin.it/wiki/Protocol_rules#.22tx.22_messages
Rule 12. For each input, if the referenced output transaction is coinbase (i.e. only 1 input, with hash=0, n=-1), it must have at least COINBASE_MATURITY (100) confirmations; else reject this transaction.
The bitcoin client might decide to wait longer, but below 100 confirmations the network would reject the transaction.