i've bought a couple of small things from the states, no full markers tho. a good trick is to get the invoice sent seperately. that way if it gets held up in customs they cant find out how much it cost. also getting the box marked, warranty returns works ok. best tip is if you've got a friend who lives in the states then get it sent to them and they can send it on. you don't pay duty for second hand stuff (apparently). also full auto markers ARE completely illegal (and if you ever use one in the uk all your hair will fall out and you'll become unattractive to women so be warned!)
hope that helps
rich