So far no downtime experienced. Really decent speed. I got the 16mb service I believe, but due to my location I only managed to sync at 7.5mb. However my mate who lives 10 minutes away from me managed to sync at 13mb speed.
I think they got their call center in UK, when I called the bloke spoke perfect English to me.
Took me 4 days or less to get connected on a brand new line (they said a week to 10 days)
And as usual, O2 got really high customer service rating.
Would suggest you either get a O2 mobile contract or O2 sim, which would knock 5 quid off your bill. It'll be quite a bit at the end of year.