Upgrading to this gorgeous little phone yesterday and I have to say I'm pretty blown away. This is my first slider phone and I'm very impressed with its build quality, weight and size (similar to the K750i but a few mm thinner).
Design
It's a very slick device. Extremely bright/clear screen. Unlike the K750i which I was coming from, when the screen is not lit up it appears completely black rather than grey making the whole phone appear black with only the silver/green highlights. The back of the phone has a slightly rubberised feel which adds to the overall quality feel. The keypad is finished in brushed aluminium and great for size, very similar to the K750i (not the new tiny buttons approach SE seem to favour at the minute) and while thin the buttons still have some travel and feel responsive for texting and general operation. One feature I really like is that with the main control buttons on the outside (two soft-keys, back, clear internet, shortcuts and joystick) you can unlock the phone and navigate through menus/internet or received message/make calls without having to pop the main keypad open. One mild annoyance is there is no way to lock the handset again without sliding it open and closed. The volume control on the side of the phone is also much improved over the K750i which for me was always a bit sticky and unresponsive.
While the coloured lights might seem like a gimmick, I've found them pretty useful already as you can assign different colour patterns to individual contacts. Which means you can know who's calling you with the phone on silent without even looking at the display if the phone is sitting on the other side of the room. They also look insanely cool in low-light settings and add a nice touch of individuality to what is otherwise a very classy phone. The themes also change throughout the course of the day to reflect day and night and I'm told there are also themes that represent the changing of the seasons. It just adds another layer of gloss to an already glossy package. The only downside to the phone is that the shiny exterior is a bit of a fingerprint magnet.
Calls, texting and general usage
First and foremost for me is the voice call quality. I've always found Sony to be a step ahead of Nokia on this front and this phone continues that. Absolutely crystal clear and a lot of room for volume to be hiked up for the most difficult of listening conditions - this is a loud and clear phone. The speakerphone is also very very good - I could leave the phone on a desk and walk around the room and still be easily heard at the other end and the internal speaker was plenty loud enough.
Texting is extremely easy and the handset retains much the same well thought out T9 dictionary as the K750i. One nice addition is that for similar words (home, good, hoof etc.) the phone seems to remember which words get chosen more often and gives them primacy at the top of the list. It also has an insanely large collection of symbols to choose from.
General menu use is extremely quick and responsive, with each menu choice from the main menu accompanied by a subtle vibration giving a nice tactile quality to the phone. The PSP style wheel menu of the Day & Night theme is a little less responsive but you can still use keyboard shortcuts to bypass any real delays. The internet is again made nice and easy to use due to the big clear screen, although it's obviously not cutting edge with the iPhone redifining web-browsing on the move. One slight anomaly seems to be the lack of pictures on the Orange home-webpage, it's just blue on white text as opposed to the Sky News pictures etc. that I used to get on the K750i.
Battery and camera usage I'm not too sure on as I've only had the phone for a day and it'll probably need a few charge cycles before it is operating to full capacity. I also need a memory stick to get pictures from the phone to my laptop as I managed to mess up the installation of the PC Suite and now it won't reinstall constantly telling me it requires a restart. I also couldn't get the software update to work over USB.
Pros and cons
+ Beautiful design
+ Screen clarity
+ Call quality
+ Very fast and efficient for every day operation
+ Build quality
- Lacks latest technology such as GPS
- 2.0 megapixel camera
- Lack of an included memory card is very stingy by Sony but 4GB of Micro Memory Stick can be picked up for <£40
Conclusion
I'm really pleased with this as an everyday phone so far, it marries usability and design perfectly and is so far the best phone I've owned. I feel that new phone joy that I haven't had for a while. I've always loved the the well thought out Sony Ericsson menu system and preferred it to Nokias so the transition from the K750i has been extremely smooth. I'd recommend it to anyone who wants a slick to operate, well put together phone that will still draw admiring glances when you take it out of your pocket to answer a call.
Photos to go up this evening when it switches over to night mode.
Now I just wish I could customise the Sony themes but it won't let me copy them to the memory stick 
