Hopefully we are the type of organization considered to be somewhat
clueful but we have yet to figure out how to get Arin to remove our swip
info from a former customer's netblock. It has been years, many many
times filling out their forms and more emails then I can count. It was
less work to get my /18 assigned then to convince them that I would like
my information removed from a /24 that belongs to someone else. 
And of course these are the kind of (ex)customers who like to get and
keep viruses resulting in a continuing effort to get our name off their
block.
Bil