i recently went with my girlfriend and her family, in the space of three days, my bike and my grirlfriends dads bike were nicked!!
Her dads one though, i have to admit, wasnt locked at the time but mine definatly was.
Luckily they were hire bikes, when we told member of staff what had happened they said not to worry and that it happens all the time!
So whether it would be wise to take your personal one or not i dont know.......
Jak