When looking at transaction details (under summary of recent transactions) on blockchain.info what is Network Propagation, and what does the value greater than 100% mean exactly?
For example Network Propagation 120% - 2168 Nodes - (Excellent)
This appears to be a problem with the way Blockchain.info measures the network propagation. Blockchain.info is not connected to all nodes in the network, it just connects to a random sample of the nodes.
So if during the propagation new connections to more nodes are opened then they may also inform Blockchain.info of the existence of the transaction, so they will be counted as well. The same goes for clients that disconnect after the announcement, they will be counted towards the announcements but no longer to the sample size.
A practical example would be that Blockchain.info has 100 connections open. Now a new transaction shows up, the nodes will start informing Blockchain.info about this transaction. While this happens 20 new nodes connect and also inform it about the transaction. So in total it gets 120 announcements, and if BC.info uses the number of connections when it first saw the transaction we get 120% nodes that saw it.
The same is also possible for disconnections. If BC.info starts out with 120 connections and while it measures the propagation of the transaction 20 nodes disconnect after they informed BC.info about the transaction it has 120 announcements, for only 100 open connections at the time it calculates the propagation.
My guess is that the second method is used. Also BC.info had some connection issues lately so a 20% fluctuation in the number of connected peers is not surprising.