Sony Ericsson Xperia X10 :: Phone Slowish Due To Multitasking And Then Crashed

I bought my Xperia X10i a month ago and it has already started giving problem. At First, It stopped getting charge then I went to the SE service center and submitted my phone. It came back with a fix and told me that your motherboard has been replaced. After 3 days, suddenly the 3 buttons below the screen stopped working. I tried updating the software through PC companion but it use to say that your phone is up to date. Then next day morning, I was browsing internet on phone and then I turned on the music, phone got bit slowish due to multitasking and then suddenly crash and after that I was never able to turn it on again. Now my phone is again with SE service center. Don't know if again I will be getting it back with a temporary fix or what, but it's really painful as my phone is just a month and a half old and already its with sony for 15-20 days in total. I am not sure if they unit test the device before delivering or not and I don't want to keep visiting SE center again and again.