[XPERIA X8 Q&A, Help & Troubleshooting] :
The procedure, simply put, usually is...

- Flash custom kernel FTF through Flashtool (unlocked bootloader)

- Once the device reboots jump straight into the kernel-integrated CWM recovery.

- Flash the ROM of your choice (from your SD card)

- Flash any addon the ROM may need for the kernel you're using

- Factory Reset ... and wipe the dalvik cache (just to be sure)

- Boot into your new Kernel/ROM combo

There's no real magic or rocket science involved, just the right steps.

The real rocket-science is rather the unlocking the bootloader part; there you have a good chance of ending up with a hard brick in case you do something wrong or you didn't check the manufacturing date ... but since your bootloader shows "r" and your device is still in a working condition ... well ... you got that right.

Getting stuck on the kernel logo just means something went wrong at the attempt to bootstrap the /system partition (Kernel is done loading and initializing and about to try and boot /system).

You can try to USB-connect your device, start a "adb logcat > logcat.log", and see if it may capture any errors why the boot stucks.

If you look into the '"General" board, there's a excellent "[HOW-TO]Report Problem and Bug [Proper Way]" thread by zackconsole.

Maybe make yourself familiar first on how that fancy adb thingy works and what kind of logs you can actually access to try and track down a problem.

When you're dealing with an unlocked bootloader it's safer to restore the device through Flashtool (though there are some major pitfalls as well). In case you run a custom kernel (read you forgot to restore the stock kernel first) chances are pretty good PCC will either not recognize your device or recognize it as a wrong device (i.e. as a X10 instead of a X8).

A major pitfall when restoring the Kernel / ROM with Flashtool is to flash a FTF carrying a wrong baseband in it (i.e. E15a where your phone is a E15i). The "Stock Kernel only" FTF just really contains the kernel.sin only ... so that's pretty safe to restore. The "2.1.1.[A|C].0.0_generic.ftf" is already slightly dangerous ... it usually carries the basebands parts in it. If there are many parts in the FTF you only select the system.sin, cache.sin and userdata.sin for flashing to avoid overwriting the baseband OR the loader.sin (<-- Boot Loader!).

So, the advantage of Flashtool, simply put, is ...

- Easier to restore the device given you have the files and you pay a little attention while doing things.

- FAST restore (PCC takes a eternity to get the job done where Flashtool only takes Minutes)

- Rooting through Flashtool (no need to jump through hoops to have the Stock ROM rooted)

Depending on how you want to go from "Restored to Stock and rooted again" ...

- Use puppet13th's x8toolbox to inject CWM into the ROM so you can flash a custom ROM through CWM (in case you're not planning on using a custom kernel, or you're in the misfortunate situation that you simply cannot unlock the boot loader)

... or ...

- Flash the custom kernel of your choice, then reboot, jump into the kernel-integrated recovery to flash your custom ROM of choice (see above).

It's really not that hard to get the stunt done; it's just knowing what you do and stick to the correct steps.