iOS 4.3 not only brought WiFi tethering to Apple devices, but it also brought the spotlight onto the carriers offering tethering services. In particular, the fact that Vodafone's Infinite plans don't include tethering in the bundled data.
As Gus over at Lifehacker points out, Voda's terms and conditions for their Infinite plans spell out that the plan's included data does not include tethering, and that data used via tethering is charged at $0.25 per MB. There is no such condition on Voda's regular cap plans though.
The bottom line is that, should you foresee the need to tether your smartphone - whether it be an iPhone, an Android or even a Windows Phone 7 device, avoid Vodafone's Infinite plans.