If there is an official ICS UK firmware for it, will it not play ball with the US keyboard?
There is no official UK firmware at all. Ultimately this phone is exclusive to the Verizon network in the states. It's just Verizon have generously decided to allow it to function on GSM networks too. US is the only keyboard layout and the only firmware option, other than CyanogenMod or AOKP.
Custom ROMs are also a bit of a problem as the phone has a locked bootloader that will only allow official kernels to load. How you do it is install a program called SafeStrap that loads just after the kernel, before /bin/init (master process on Linux systems, responsible for starting everything else) and lets you have the kernel boot a different /bin/init from another partition. This means you'll get the CM9 or AOKP framework, software and apps but you have to use the stock kernel which probably doesn't support overclocking. Edit: Someone has made a loadable module for it to allow overclocking. Not tried it myself.
So far I have not managed to get data working on either CM9 or AOKP but apparently I just need to change one setting in build.prop. I will investigate more tonight as the vendor bloat in the stock ROM is pretty bad.
I am still happy with the phone though. Yes it was a faff to set up, yes I nearly bricked my pants when I thought I'd bricked the phone but in reality I'd just flattened the battery while in the middle of installing CyanogenMod and it was the battery preventing boot! Yes the vendor bloat is annoying...
...but then a text message arrives, and you tap out a reply on that wonderful 5 row keyboard, and all these problems just go away... If you're a fan of QWERTYphones it is totally worth it.
Once I get AOKP running I'll update this thread with further instructions.
It's also worth noting that when the official ICS firmware is released, most of these problems should go away. Should just be able to flash via an official OTA update, skip the Verizon activation process, insert your SIM and away you go.