Decided to check mine out and found out that I have a crack in mine...
Be sure to check out your X1, if you have a crack send me a PM with a photo and the color of your X1 as well as the production week, branded or unbranded and the country you bought it in.
There have been other people reporting to have the same crack, as well as a crack in the battery compartment (I am lucky to not have that) but be sure to check it out for yourself:
I just found out a few days ago that my case has started to show more cracks. Ever since I discovered the initial cracks in my case I haven't touched my stylus, and check above what happened... I am so pissed off right now. Also because of the super bad service from the T-Mobile shop, who still hasn't called me back.
A picture from another users, who has a nasty crack in his phone. As you can see it is from week 44, mine is from the same week. In regard to my previous edit, another crack has formed near the other side of the stylus insert and the paint is starting to come off now. Maybe we should write a letter to Sony Ericsson and ask them to take all the phones from week 44 back...
Bad Xperia list:
The info I will put up is: username: branded or unbranded (country), production week -> type of crack / other fault
01. vincew: Silver T-Mobile branded (Netherlands), 08W44 -> cracked near stylus at two places, paint coming off
02. wickedwy: Silver Unbranded (Netherlands) 08W44 -> cracked at the back
03. LZF: Silver Unbranded (Netherlands) 08W44 -> cracked at the back
04. andyboo - Silver (UK) 08W?? - stylus
05. comeradealexi - Black Vodafone branded (UK) 08W?? - cracked near stylus
06. Dryw Filtiarn - Silver 08w?? - cracked near stylus
07. boomdijk - Silver 08W?? - cracked near stylus
08. jeehaa1 - Silver Unbranded (Netherlands) 08W46 - cracked near stylus
09. brewspec - Silver T-Mobile branded (Netherlands) 08W?? - cracked near stylus
10. markda2000 - Silver 08W44 - cracked near stylus
11. Ganondolf - Silver Unbranded (UK) 08W43 - cracked near stylus
12. hvsanten - Silver Vodafone Branded 08W44 - cracked near stylus
13. YYYYY - Black 08W42 - cracked at the back
14. jackleung - Silver 08W44 - cracked at the back
15. bigmouth66 - Silver T-Mobile branded (Netherlands) 08W44 -> cracked at the back and more
16. geertbargeman - Silver (Netherlands) 08W44 -> paint coming off near stylus
17. kakalak - Black 08W46 -> cracked near battery and another pic
18. myriade - Black unbranded (Germany) 08W45 -> Plastic broken out on the side
19. VampiruX - Silver unbranded (France) 08W44 -> Cracked near stylus
20. blitz82 - Silver T-Mobile branded (Netherlands) -> Cracked near stylus
21. experia1234 - o2 branded (UK) 08W46 -> Cracked near stylus
22. m@rco - Silver T-Mobile Branded (Netherlands) 08W44, Cracked near stylus
23. emwdava - Silver (Sweden) 08W39, cracked at the back (battery compartment
24. endebe - Silver Vodafone branded (Austria) 08W46, cracked on the side
Update: Jan. 21 2009
I've stopped updating the list of cracks, simply because I do not have the time anymore. What I did with my X1 is send it back to T-Mobile and after 10 working days I got a brand new one. I encourage all that have a crack in their phone to contact the seller and get a replacement. This is a common and acknowledged problem, you should be able to a get a fixed one or a replacement under warranty.