Why doesn't the magical world have something resembling the internet? There are a few things resembling closed networks--the dark mark, Quirrell's monitors and other tricks for the battles, and canon Hermione's trick with the DA Galleons--and there are simple two-way communication methods, like the floo and the two-way mirrors, but the only military use of networking that we know of is the dark mark (and the DA Galleons in canon). This makes me wonder if the power of the dark mark wasn't just that it was terrifying and exerted mental influences, but that it's a secure means for Voldemort to coordinate his forces without requiring individual conversations or everyone gathering in Malfoy Manner. (In canon, it seems to have mostly been used as a signal to meet up, but surely a smart Voldemort would recognize its other uses? Even if it can only send one bit of information--touching or not touching--it could still be used to encode useful messages. Hermione's Galleons actually sent and stored a few bytes of data, and it's a little worrying that they weren't used in Deathly Hallows; did Madeye think Voldemort could hack into the network, or something?)

I suppose the question is: if Voldemort and canon Hermione can create useful networks, why didn't the Order of the Phoenix or the DMLE develop something similar? Even if you must be at least Hermione smart to manage this, the Order had Dumbledore, who studied the dark mark (perhaps it was too little too late in the first war, but if MoR Dumbledore hasn't set up the OotP with a magical LAN after TSPE, I'll want to know more about why it doesn't happen. Too much like the dark mark? Has Magical Britain never heard of an arms race?)