The wizarding world (and you know which wizarding world I'm talking about) has flying motorcycles. They've improved on our photographs by making them move. Instead of airplanes they have apparition. Instead of typewriters they have quick-quote quills. Instead of cell phones they send messages with their patroni (patronuses?). Instead of internet they have...wait--they don't have anything! Rowling, are you trying to tell me that these wizard and witches who live amongst muggles don't have an alternative to internet? Surely they've noticed their muggle neighbors looking at funny metal and plastic boxes; I know Harry has been on Dudley's computer. Why haven't they adopted this muggle technology? I'm quite certain they would find it useful. Email is faster than owls, for one thing.
Imagine if the Quibbler had been a blog. Imagine if Voldemort's Wikipedia page were getting vandalized by people typing, "Dumbledore's Army now recruiting!" or "Support Harry Potter!" Imagine if Death Eaters tracked who was looking at Harry's Wikipedia page. Imagine if information on horcruxes could be scoured for through Google.
Edit: I think the seventh book is supposed to take place around 1998, so I guess internet culture wasn't quite as large a force then. But still, I feel this is an oversight on Rowling's part.