After moving from Orange - and their 30-40 min telephone support waiting times - I am always surprised to get through to an o2 support rep almost immediately... I mean, really, I am always shocked when they answer. And I don't miss Orange's hold music either!
Their email support is hit and miss. If they don't understand your query, or don't want to understand it, they just give you a generic template response and hope you'll give up. I just phone them, it's often easier.
So yeah, I don't know if the phone support joy will cease now that there isn't a dedicated "press 1 for iPhone" line (I think there isn't anywho), but good so far.
Nothing much else to commend or compain about. Reception sucks but I'm pretty sure that's the iPhone v1 for you (other o2 phones perfect in my house)... Oh, I forgot: I'm sure I've sent 'STOP' to their text marketing a few times now, and it carries on regardless! but no biggie.
All round: good experience so far. I'll definitely be upgrading to 3G and happily signing up to another 18 months. (great value pricing for next gen handset and service plans too, in my opinion).