Thanks to a simple patch that was applied yesterday from the kernel mailing list, the ipheth driver now supports the Apple iPad. The ipheth driver is the iPhone USB Ethernet driver for Linux. This open-source driver allows iPhone (and now iPad) tethering via USB cables and doesn't require a jail-broken iOS or third-party proxy software.
Up to this point the supported ipheth hardware has been the Apple iPhone 2G, iPhone 3G, iPhone 3GS, iPhone 4, iPhone 4 CDMA, and iPhone 4S. Before getting excited about the iPad working, be forewarned that it's only the original iPad -- not the latest-generation iPad or even the iPad 2, but the original first-generation iPad (product ID: 0x129a).
The ipheth kernel driver has been mainline for over two years now and the driver is to be used in conjunction with its user-space component to perform the handshake and device pairing, etc. More information on this Linux iPhone Ethernet driver is available from this web-page.