I know that it seems like a lot of you guys are having real trouble - and I really don't want to gloat, but the process has worked for me, and I thought it might be note worthy to let you know what happened:
7:36am - recieved an email saying that 'The iphone is here' and 'taking online orders from 8am'.
8:20am - woke up, check email (no idea why, must have been a sign!) started online form filling. Selected 16gb black.
8:48am - Thank you for your O2 order email. "We're just currently processing your request and we'll be in touch shortly to let you if it's been accepted and when it will be dispatched."
1:15pm - Phone call from a very nice lady at o2, credit check with driving licence and/or passport. Address check with credit card. All okayed. Confirmed that iphone will be with me before 10am (additional cost of £10) on Friday. Try not to get too excited or tell anyone for fear of being called a loser/being mugged/spat on/counting chickens before they've been delivered.
14:20pm - Read posts about poor pre-order service from o2. Feel guilty that its been so smooth for me.
14:30pm - Write this post, and hope that O2 corrects the proceedure so that everyone shares the same experience as me.
14:35pm - Realise that I'm actually employed and should do some work or I won't be able to pay for my contract...
FYI, I'm a new o2 customer, moving over from Orange. I was planning to buy from the store, but decided to preorder when the email came through.
I hope this helps/is of some interest/doesn't fuel any rage!