Hi,
You 'could' use the US version here in the UK, but it'll not auto connect to any of the UK banks automated statement download service. Also, things like UK specific financial and monetary aspects will not be supported/covered - things like ISA's, VAT (if you are a small business), UK share ticker feeds etc etc.
If you simply wish to manually track a bank account(s), credit card account(s), your mortgage, then you could 'make' the US version work for you.
I used to work for Intuit and was involved with the Quicken product in terms of development, Testing, Support and Consulting, and know the software very well(main experience being the UK version but I also had to know quite a bit of the USA and other territory specific versions). The UK version was withdrawn in 2005, due to lack of demand. I still provide a support and consulting service via an ebay advert and I just remembered to bump up a thread here on UKY as well.
Specifically for Americans who are here or indeed travel regularly and have various interests in the UK, USA and further beyond, I'd very often speak and deal with users for specific nuances and scenario's. It's been quite a while now, but the 'basics' are still pretty much the same. I'd suggest perhaps using the last UK version to cover your financials if that's most prudent with your individual scenario. If you need a 'mix' of using the UK and USA version, I can still offer some pointers. Drop me a PM if you wish !
Cheers, DtM! West London & Slough UK!