Problems. Poor locality of reference. Possibility that the value you set and check are unrelated. Meaningless variable name making it hard to know what the flag means - people often write code thinking the flag means X when it is true, and then slip up and treat it as NOT X instead.
in reply to Flag variables
Not all flags are bad. But make the flag's name a yes/no question which its value is the answer to (avoiding reversing its meaning), and don't use a flag where an alternative suggests itself.
Additional misfeature in your code. The &foo notation passes implicit arguments which is often not desired. As perlsub says, This is an efficiency mechanism that new users may wish to avoid. *ahem* Experienced users as well. :-)