Just switched from Sky to o2 for my broadband and I must say, what an excellent service.
My exchange has only just got o2 in which is why last year I went with Sky and to be honest Sky was good value for money.
I got my mac from Sky and ordered o2 online on Wednesday evening, router was delivered Friday morning and switched on by the following Thursday.
So 1 week and plenty of text messages to keep me up to date. No charges at all, just the subscription.
I got a naff phone line but managed to get an extra meg of download and upload went from ~400 to ~800. Took a static ip and now paying £12.50 pm.
Had a little issue getting connected but spent an hour on to tech support who were real helpful, answered call straight away and on an 0800 number.
o2 comes highly recomended.