I bought the new (Samsung) Google Nexus S this week. I have to say that it is amazing! It is faster and more responsive than anything I have tried. The only problem I had was that the mobile internet was not working with the retrieved settings.
After googling the hell out of this, checking the manual settings on the O2 website, and even calling tech support, I finally figured out that the settings on the website AND the ones tech support told me were wrong.
Without any further adue, I give to you...
APN type: internet
If you're having this issue, hopefully these settings will do the trick.