Just to clean the engineers' image :)
(Though I am not one...)

The term 'finite' in the expression 'finite probability' is not in opposition to 'infinite', but 'infinitesimal'. It won't make sense to talk about infinite probability, but it is often the case that the likelihood of an event is evaluated via limits. Once the value of a variable approximates the limit, the probability of an event is shown to be zero.

Aswath,

I won't come swinging, but a huge difference is that here are no superndes with Peerio, and that Peerio is an enterprise offering initially and it's not likely that an enterprise will all go offline.

Also, the way Peerio distributes content versus the way Skype does are likely different, otherwise they would be infringing on Popular Telephony's patents.

Remember, Skype is a consumer communications platform first.

Doesn't it just suggest that Skype has made their space/bandwidth/reliability tradeoff badly? I mean there's LOADS of free space on the average laptop, and spreading the message out a layer or two and directing it to a few hundred buddies with one or two degrees of separation from the recipient can't be that difficult. To me this is just a matter of making the P2P network do it's own "O&A" -- identify isolated or overloaded nodes and send traffic elsewhere. Still a PhD distributed computing problem, but I think they can afford a few bright folk now, don't you?

Andy:

You say Peerio does not have supernodes and I say every node is supernode. :-)

As far all nodes going offline, it is all in deployment scenario. If they are standalone devices, yes one can assume they will not all go offline. But what if they are softclients? Nonetheless, the point is there is a non-zero probability that all the storage nodes have failed. This event may amplify if the operating assumption changes, if temporarily. I am not sure that one can device an operating policy to handle all situations, as Martin seems to suggest.