I'm just back from the O2 shop at Ocean Terminal with a shiny new iPhone 4 and thought I'd jot down a few impressions of the device:

• The screen is absolutely stunning. I've never seen a display as crisp as this thing and I certainly can't pick out individual pixels without holding it up to my face and peering into the screen. Whether that says more about my eyesight than the actual hardware remains to be seen, but I'm not disappointed. Text is astoundingly sharp on web pages and in iBooks. The little app icons inside folders are clearly identifiable now too.
• It's fast. Paging through home screens and launching apps is a complete joy compared with my aging launch-day 3G. The initial restore from backup and sync process in iTunes was significantly faster too (highly refreshing after dealing with the slow fortnightly restores during the iOS4 betas). It remains to be seen just how this stacks up with the 3GS and the iPad, but given that the A4 is powering it, I've got pretty high hopes.
• It feels solid and professional. Next to my 3G, it's clear this device is in a different class. It looks right at home next to the aluminium and glass MacBook Pro, feeling much more like a professional product than the plastic iPhone 3G. The iPhone 4 is about the same length as the 3G, but it's only as wide as the 3G's front glass panel. My once futuristic and sleek 3G feels big and clunky in comparison. The significantly improved build quality makes itself apparent as soon as you open the micro SIM slot.

Once the micro SIM is activated and I'm using it properly as my primary phone, I'm sure I'll follow this up with some more thoughts on the actual hardware. From the service perspective, I couldn't be more impressed with how painlessly O2 handled my upgrade. As an existing pay monthly customer, it was a simple case of confirming my identity, choosing a plan and paying for the handset. After finally getting in the shop (after almost two and a half hours, thank god for the iPad and the WWDC sessions!), I had a bag in my hand within about 10 minutes. Easy.