Vodafone UK go unlimited for data!

I've just received this text on my phone: "Good News! Your monthly data allowance is now unlimited so u can use mobile internet & email every day. Fair use applies. More at vodafone.co.uk/mobileinternet" Looking on the link supplied, I see the standard price of £7.50 is unchanged, but there is no mention of 120mb anymore - only unlimited. Also, the cost if you add it to your contract (ie: can't remove it until your contract expires) is just £5! Not bad for a free upgrade. I suspect ther