i totally agree-people used to say to me "oh my god i love your top/bag/jacket, where's it from??" and now it's "that's from primark" (accusing look) the best one i've been to is hammersmith in London-2 stories!! (really great homewares as well!) but my local is kilburn, london which is always so busy it looks like a jumble sale
(so obviously Primark is in London but never anywhere really central like oxford street which keeps it a little more secret I suppose, it's originally an irish store though!)