I don't blame the MiFi: At Apple's flagship Worldwide Developers Conference (WWDC) keynote this morning, Steve Jobs had to more or less demand that attendees disable their MiFis and similar devices, because the sheer volume of unique Wi-Fi networks was preventing the proper functioning of the iPhone 4 for demonstration purposes.
The new iPhone 4 has dual-band 802.11n, so it's beyond me why Apple didn't prepare to use a 5 GHz network channel, since the MiFi and similar devices nearly all only create a 2.4 GHz base station either by design or default.
Update! The iPhone 4 specs are posted, and it's 802.11n in 2.4 GHz only. There apparently wasn't room for a chip with two bands and the necessary antenna. (Thanks to Micheal in the comments.)
InfoWorld has the count: 527 Wi-Fi hotspots were in operation in the keynote address, most of them MiFi, and over 1,100 devices connected among those and other shared Wi-Fi networks.
A few weeks ago, Google suffered a similar embarrassment in demonstrating Android 2.2, a new release of its smartphone software, in which the audience's heavy use of the Wi-Fi network required presenters to ask (more nicely) for people to stop using the Google-provided network.
At the iPad launch in January, Apple offered its own Wi-Fi network, which worked just fine for me, and likely reduced the use of 3G cards and MiFis. [Update! Apple did have its own public Wi-Fi network at the keynote, but everyone I spoke to did not trust it (they thought it might be a spoof network) and did not use it.]
Clearly, Apple needs to make its iPhone OS (renamed iOS this morning for its next release) better able to handle a truly ridiculous RF environment.