I've got a HUGE purple leaved Berberis bush outside my utility room window and I tell you, if I ever get burgled they WON'T be getting in through that window! The thorns are vicious!
I get tiny 'sproglet' plants growing through the gaps in the paving beyond, which I often gently (with gloves!) pull up and repot to grow on, but I have to say I don't consider it an invasive species at all.
As Susie says, it's a great deterrent, plus very spectacular visually, and good for feeding birds (a lot of little sparrows roost in mine - presumably feeling safe from cats in there!)
If you do want to get rid of it, do offer it to other householders - they cost good money in garden centres!!!!