So lets' start...:
PS Store can be accessed with a UK account but you would not be able to purchase anything (credit cards are not accepted - from Bulgaria/Romania - I live in Romania).
If you really want to buy DLC you have to try a US account, where SOME of our credit cards get accepted!
HOME - UK account.
VIDZONE - UK account and a proxy server from UK, vidzone access is restricted with country filter and IP filter!
I recommend using a UK account for all of the above, being that aditional DLC requires same region games, so if you have KILLZONE 2 PAL the DLC from US will not work!
Simple really, but maybe with time we won't need all that... We are part of UE and no one seems to care...