[XPERIA X10 Q&A, Help & Troubleshooting] epinion:
In this thread I would like to gather usually asked question. Feel freely to add more. And I will add more too. Any suggestion or correction welcome. Here we go.

Q: I want to flash my phone to other ROM. What should I do?

A: You could refer to this post about X10 Flash Tool by Bin4ry and list of the ROM from here by jerpelea

Q: I want to flash my phone but don't want to loose my apps and settings

A: Just don't include userdata.sin when flash. Thanks to MarylandCookie

Q: I restore my contacts using stock Backup and Restore Apps but I can't see my contacts in the phonebook.

A: The apps restore the contacts under your Google accounts. You could show your Google contacts by Clicking three people icon at the top left of your phonebook and enable it from there.

You should check about Social Phonebook too.

Q: My market keep crashing when download apps. What should I do?

A: Go to Settings -> Applications -> Manage Applications -> Find your market apps -> Clear cache (if any) -> Uninstall updates

Q: I want to remove ads from apps. What should I do?

A: IMO, just let it be. That's what make so many android apps free.

Q: I need to root my X10. What should I do?

A: Use z4root. Refer to this post by MarylandCookie for detail

Q: I couldn't find Assisted GPS option. Where is it?

A: Settings-> Location and Security -> Use wireless networks

Q: Where is the Auto Brightness?

A: Brightness except 0 and 100 IS auto brightness just work different way. Or you could try using Spare Part apps from the market

Q: I want a longer battery life what should I do?

A: 1. Turn off GPS : Settings-> Location and Security -> Uncheck Use GPS Satellites

2. Turn off Wireless Networks : Settings-> Location and Security -> Uncheck Use Wireless Networks

3. Use home launcher replacement such as ADW Launcher by anderwerb, Launcher Pro, HelixLauncher, etc

4. Make your phone in airplane mode after 23:00. You could automated doing this by using Timerrific apps

5. Turn off your Autosync : Settings-> Accounts & sync -> Uncheck Auto-sync

6. Turn off/make a longer interval of your update. Such as Facebook, Twitter, etc. Usually there is an option for that inside the apps itself

7. DO NOT Use AUTO Killer apps. Use a MANUAL Task Manager. Kill the apps manually when you feel want to do it. Do not need to do it automatically or often though

8. If you have unstable 3G networks, change your phone to GSM Only : Settings -> Wireless and network -> Mobile Network -> Network Mode -> Choose GSM only. Switch to 3G network/WCDMA when you need it and don't forget to switch back, because unstable signal could drain your battery

Q: I want to optimize my X10. What should I do?

A: 1. You could applied Jit. You could find it from here by ttxdragon or here by jerpelea

(I just enable Jit and manually delete app I don't want. Well I keep Timescape and MediaScape ^_^ )

2. In my observation, no need to change the Heap Size, because 24 is the best value fit for our X10. Otherwise is just a placebo effect. Even I experience have to click little apps more than one to run it when I'm in 32.

Q: I don't what apps are safe to delete. What should I do?

A: You could try to see the list here by exekias

Q: I wrongfully deleted my system app. What should I do?

A: You surelly want to try to install it again from here by XperiaX10iUser

Q: I cannot receive SMS when there is Low on Space notification

A: Probably Solution : Use Titanium Backup and choose Clean Dalvik Cache. Haven't have time to try it yet.

Q: I want 3D Gallery. What should I do?

A: Use ADW Launcher or Launcher Pro (I only tried those launcher) and add Custom Shortcut, Choose Activity, and you will Find Gallery from the list. That's is your 3D Gallery

Q: I want hidden Music app. What Should I do?

A: Use the same method as above only choose Music this time. IMO it's not that great, as matter of fact I deleted the "hidden" Music app. ^_^

Q: I'm bored with the look of my phone. What you need is theme.

A: 1. Read _calum_ theme reference

2. XperiaX10iUser's theme

3. Theme from dk2000zx

4. Elemental theme from Mr_Element

5. Or you could just go to this section. There are plenty of them. ^^

Q: I want 2.2 for my X10.

A: There is no official announcement about it.

Q: I still want 2.2 for my X10.

A: Well you could just try it from this thread

Q: Ouch I forgot to bring my cable. My cable is missing. My cable is broken. I need to access my phone using ADB. What should I do?

A: You could try using ADB Wireless

Q: Is there any recovery menu for X10?

A: Try to see this thread

DISCLAIMER : USE WITH PRECAUTION AND AT YOUR OWN RISK for applying every ROOT operation.