I have been using Sony Ericsson Xperia Mini for more than two months. So far, it is doing very well. It is an amazing phone for the price range.
It sports a 1GHz Scorpion processor, Adreno 205 GPU and a 5mp camera with HD video recording. No other phone in this price range offers this kind of specifications. The touch screen is very responsive. User-experience is very good. I have never experienced any lag. And the phone is very much pocket, thanks to its small dimensions and weight. I would recommend it for anyone considering my experience. The Android version is 2.3.3 Gingerbread and 4.0 Ice Cream Sandwich update will be out next year, which will make this one the only phone, against the competition (as of now), to get ICS update.
To my knowledge, Xperia Minis, at the time of releasing, had the problem of capacitive buttons getting activated after using the phone for sometime. I think it is rectified now as I have never experienced a problem like that.