I have had the X10 for almost 2 years now and I think it's about time to ditch it for good.
But since Gingerbread I'm quite satisfied with the X10, the only problem I have is that the phone/battery heats up and then starts random restart cycles.
I was home all day today and that's when I never have an issue with it, only when I'm out and listening to music and try to browse the web or taking pictures it would just freeze and restart.
That's a reason to get rid off it.
For Xperia S, I might actually wait until Ice Cream Sandwich is out.
I have learnt my lesson when I bought an outdated 'Donut' device and got the update 6 months later with the X10.
The GSIII seems quite a stunner as well, so I am a little bit undecided but I guess that I will treat myself to an Xperia S in the coming days/weeks because I have been loyal to Sony /SE for a long time.