[Groxx]

In a very technical sense, yes. And miners can choose to not include your transaction in the block (ie, if you don't meet the fee requirement they chose). It's entirely possible for your transaction to be continually pending and never accepted.

In practice, it takes within about 10 minutes for the first confirmation to go through, and 10 more for each one after that. Most merchants will likely be interested in waiting for a few more blocks to be added before totally accepting, but that can be solved by middle-men that provide insurance against double-spending, allowing immediate transactions. And transactions move across the network quite quickly - I tend to see them appear well within a minute.

[erikpukinskis]

I don't see why waiting for blocks is necessary. If a large portion of the network consenses within some small number of seconds, the likelihood that a rogue portion of the network would confirm conflicting transactions and then have that confirmation confirmed by that consensing network is vanishingly small.

[Groxx]

In general, yes. But I do somewhat doubt that it'll be seen that way by many merchants - greater confidence they got paid is... greater confidence they got paid. Especially for internet purchases, a 10-20 minute delay is often unimportant.

[tptacek]

Am I reading that right? On Internet purchases, 10 minute delays are unimportant? I chose who to buy Cisco routers from because of the specter of a 5-minute delay. Can you flesh that statement out a bit?

[Groxx]

Essentially that the shipping time utterly dwarfs the validation delay. The main place this wouldn't be true is if you purchase an online activation key of some kind - if you purchased a downloadable, it'll often still take more than 10 minutes to complete.

The moment you send out your transaction (assuming it's valid), you can consider it approved, and move on with your life. The recipient can also acknowledge the transaction within a minute or so at most, it's the network validation and protection against alternate transaction histories that takes time.

[erikpukinskis]

FWIW, there's a pretty extensive discussion of the fast transaction problem here: http://forum.bitcoin.org/?topic=3441.0