I think owning a Focus ST depends on A what you have owned before and B how old you are.
I bought my focus ST when i had just turned 19. They look great, Sound great after a couple of mods, go well everything a 19 year old could want however the build quality of these are not the best. mine was a 07 and had many squeaks and rattles, i now have a 53 plate Golf R32 which has absolutely no squeaks and rattles.
I would probably not own another focus ST due to the build quality i think. If you have to even think about fuel consumption do not bother getting one. In my opinion theres no point in buying a powerful car to not be able to fuel it and then if you go on the motorway sit in the slow lane doing 60 to get "good MPG" its pointless.
The last thing i have noticed from the STOC forum/Facebook page a lot of 'Chavs' seem to be attracted to the focus ST 'I raced this' 'I raced that' seems to pop up a lot.
Im 20 nearly 21 and much prefer the refined Volkswagen these days.