Just picked one of these up to replace my previous phone and so far VERY impressed. It comes with Android 2.3.4 (Gingerbread), but Sony Ericsson have stated that it will be getting an update to Android 4.0 in the near future, so it's future-proof in the short-term.
What I like:
* The Display, really nice colours and the Bravia Engine really does enhance the richness of colours nicely.
* The speed, it's got a 1.4Ghz CPU in it, so when it needs to, it can really fly. Everything feels smooth as silk, no lag or anything.
* The camera. REALLY good easily one of the best cameras in smartphones today, blows away anything Apple can offer up. The Panarama shooting works very well once you get the hang of it. It can do 3D pictures too (but I don't have a 3D TV to test this out). There is a camera button on the side which makes it feel like a proper camera, and it has all the usual features of Sony cameras, face detection, smile detection etc etc.
* Battery life. For such a powerful phone, the battery life is actually much better than I had imagined. I'm getting WAY more out of it than my previous smartphone. Easily a day of hard use, and two of medium use.
* Design, this phone is a very slim sucker.
What's not so good.
* Bundled apps. Some can be removed, others can't. (Please Sony, sort this out, we don't want alot of the crud). Fortunately you can root the phone and remove them. But users shouldn't have to do this.
* Design, this phone is a very slim sucker, and it's easy to mishandle and drop, especially when using the camera. You can get a rubber-feel back cover to make to more grippy and there is a hole for a wrist-strap (not included) if you have problems in this area.
Easily one of the top 5 smartphones of the moment (Nov 2011), however it doesn't have the price-tag of it's better known peer products (iphone4s, Galaxy S2, HTC Sensation), so is a bit of steal.