Understanding speed vs. fees on various wallets, esp. Instawallet and original client The Bitcoin Wiki don't say much about fees, more precisely if you have a choice between speed vs. fees (pay more, deliver faster).

In fact, I don't yet even have a clue how fast are bitcoin transactions. Sometimes instant, sometimes it is structured by the wallet provide for lower fees but takes up to 24 hours?
A wallet provider might make it seem like the transaction is instant, but it will have to be included into a newly mined block (happens about every 10 minutes), for it to actually "go through". If you only pay a low transaction fee, it might take some time until a miner decides to include your transaction.

After that, it's up to the receiver of the transaction to decide how many blocks to wait until he books it as confirmed on his side.

The default client waits for six of these so-called confirmations to show the transaction with a checkmark.