The same thing happened to me, placed the order, then ignored the order confirmation page as I assumed I would be emailed everything I needed to track the order. No email came through. No details on the order page within my O2 account.
Called Customer Services and they confirmed the order and gave the order number. I don't think they have the phone in stock though, it's the HTC HD7 which was released on the same day as I ordered. So I'm thinking the common denominator here is: no confirmation email if the system says it's not in stock. But I could be wrong.
Baffles me why O2s poor website/systems put strain on the call centre in terms of volume of calls.