Xperia X10 android phone has been rooted successfully. Bin4ry over at xda-devs managed to get the root access on Xperia X10 and have posted easy steps to follow.
Steps to root Sony Ericsson Xperia X10 Phone
1. Download (from here) and unzip the file.
2. Read howto.txt and find your DeviceID in the registry and change the DeviceID.txt in step1 and step3 folders.
3. Now run step1.bat. This will update the phone firmware to R1EA018 S0-O1B.
4. After flashing, remove the battery and wait for 5 seconds.
5. Replace the battery and reboot the phone.
6. When phone is running again activate USB-Debugging.
7. Do a factory reset (recommended).
8. Then run step2.bat. A popup menu should appear.
9. Choose option 6.
10. The phone will reboot and flash. After an end and everything will be ok.
11. Now run step3.bat. This step will update the baseband X10i R2 (this is for X10i only).
12. After you finish this. The phone will restart.
13. Now run step4.bat. This will allow the root, and delete SE and Docomo Stuff from phone in addition to installing small apps.
Voila! Xperia X10 has been rooted successfully! you now have the rootshell on your Xperia X10. If you found these steps hard to implement, you may follow the 10 minutes video guide on how to root your Xperia X10. Just check it out!
Video: How to root Sony Ericsson Xperia X10