You're not the only one. I've owned the handset for nearly 2 years now (I'm on my 3rd replacement due to overheating and microphone issues) and I've never had a phone as bad as this one. The performance is absolutely abysmal. I'm running the stock Vodafone UK 2.3.3 FW, I've rooted, removed bloatware, even uncapped the framerate and still the performance is absolutely unacceptable. I've tried (and paid for) all of the top name launchers in a bid to stop my homescreen icons having to redraw everytime I return back to the homescreen from browsing the web or reading a book via Kindle. None of them have helped.
I'm currently using the stock launcher and even that hasn't helped at all.
Most of the time I can't answer calls because the screen won't switch on quick enough. When I want to make a call (using the stock Dialer) I have to wait anything from 5 to 10 seconds for the damn thing to load - a phone that doesn't even really work as a phone! It's terrible!
My contract ends in August and I'm seriously considering either starting a new contract with another provider early in order to get a handset that works (the HTC One S has caught my eye), or just buy a SIM free handset (a Nokia 5110 would be better than the Xperia piece of s***) just to tied me over till my contract ends!
Believe me, Disappointed, I feel your pain!