To get from 3.0.1 Non-US image to a US image (GED) - I followed the following steps... please note - it is highly recommended you do some Google searches, and/or search XDA for if this will work on your region if you are not on a UK based Xoom...
1. Back up any stuff you want to a PC, make notes of apps you might want to re-install etc. This will wipe and factory reset the Xoom including storage on the Xoom
2. Unlock the device via Fastboot:
2a. Download the Motorola USB Drivers from here: http://developer.motorola.com/docstools/USB_Drivers/ (you may need to sign up, but can probably find these elsewhere via Google if need be.)
2b. Download the Android SDK from here: http://developer.android.com/sdk/index.html (you only really need fastboot so might be best to grab the zip version), else you may need the Java SDK too.
2c. Power off your Xoom
2d. Press and hold Volume Down while pressing (and holding) the power button to turn on the device (you can let go of power when the device comes on)
2e. Open a command prompt window (cmd)
2f. browse to your sdk\tools folder, i.e. c: -> cd sdk\tools etc.
2g. type: fastboot oem unlock
2h. Read the warning on the Xoom screen, Volume Down button to change selection, Volume Up to select.
After 2. you will be unlocked, but have no warranty from Motorola unless you lock again (fastboot oem lock) with your region's image.
3. Flash the Official, complete US 3.0.1 HWI69 Image
3a. Download the Image files here: http://developer.motorola.com/products/software/
3b. You will probably want to grab a copy of your region's image if available, as well as 'Build HWI69 for US Retail' image: http://developer.motorola.com/products/software/MZ604_HWI69.zip/
3c. Extract the .img files from the zip, boot.img, system.img, recovery.img, userdata.img and put them in the same location as fastboot.exe (for ease)
3d. You should still be in fastboot mode (from 2), enter these commands one at a time followed by enter/return (waiting for them to complete before running the next command):
fastboot flash boot boot.img
fastboot flash system system.img
fastboot flash recovery recovery.img
fastboot flash userdata userdata.img
fastboot erase cache
fastboot erase userdata
(DO NOT RUN fastboot oem lock as written on the motorola developer site)
3e. Reboot device either with hold Volume Up and Power, or fastboot reboot
3f. Run through and set up the device as new.
4. OTA Update to 3.1
4a. Either let the system update itself OTA (took me about 5 minutes for it to come down) and follow on screen instructions to update to Honeycomb 3.1
4b. OTA file is available here: http://android.clients.google.com/packages/ota/motorola_tervigon/e379f0b9bcd0.signed-tervigon-HMJ37-from-HWI69.e379f0b9.zip
4c. If you are interested in Rooting, custom kernel etc. read this post: http://forum.xda-developers.com/showpost.php?p=14237506&postcount=7
5. OTA update to 3.2
5a. Either let the system update itself OTA and follow on screen instructions to update to Honeycomb 3.2 ... or... my OTA had not come down after about 2 days, so found the next method to work (you will need a USB flash stick, and an OTG USB Host Cable)...
5b. Download the OTA from here: http://android.clients.google.com/packages/ota/motorola_tervigon/db223b6ed7c4.signed-tervigon-HTJ85B-from-HMJ37.db223b6e.zip
5c. Put the .zip above on to the USB flash stick.
5d. Power off the Xoom
5e. Plug in the USB flash stick to the OTG Cable and into the Xoom
5f. Power on Xoom and tap Volume Up when Motorola splash screen is on and it should have a bit of text at the top left showing 'Recovery'
5g. When you see the Android logo with the exclamation mark, hold Power button and tap Volume Up to enter Recovery
5h. Volume Down, to select 'Apply update from USB drive'
5i. Press Power to select, and let it apply the update. If it fails try re-downloading the .zip
5j. Reboot and you should now be running Honeycomb 3.2, stock, US image.
6. Real English (UK)... and other languages.
6a. If you want to set yourself up with English (United Kingdom) not English (American), then you can download an apk from the market to help,
6b. Look for MoreLocale2 from the Market: https://market.android.com/details?id=jp.co.c_lis.ccl.morelocale
6c. Open the App,
6d. Click Options (grid icon)
6c. Add Locale
6d. Label - English (United Kingdom)
6e. Language -en
6f. Country - GB
6g. Click Add and set this as your language.
I don't think this helps with the 'Using an external keyboard still uses the US layout' issue, but if I find a solution to that I'll update/post an update with that.
If you want to root - see here: http://forum.xda-developers.com/showthread.php?t=1170760
Thanks go to XDA Developers, masterslacker, poisike and iammodo (all from XDA) for various parts of this.
Random Rambling/History behind the above:
Having had a Motorola Xoom from launch (in the UK), one thing that fairly quickly started to annoy me was the soon apparent fact that Google's Experience Devices (GEDs) like the Nexus range, didn't seem to apply to the Tablet world, apart from the US Xoom's. (Verizon's 3G and US WiFi models it seems).
Motorola have to modify/develop/push out the updates to anyone else in the world, including Canada and the UK.
If I had realised that at the time I might have thought twice about letting Motorola look after the needs of the Android tablet community, and chosen a different tablet.
Also that they took ages to release the original images for the non-US devices which meant any tweaking or playing could result in non-recoverable bricks...
Luckily - the hardware in the US WiFi, and the Non-US WiFi are identical so the images happily go straight on top - although I, as well as others, were reluctant to flash US Images to the Non-US models because there was no return... until the day after I gave up, flashed the US image on to my UK Xoom and then they released the images - hurray - now we can go back when/if we want to!