Pst, Marak: have you noticed that anytime you make an uncalled for perception roll, something happens? Gangers spying on us at the warehouse, Mr. Scary Man, etc.?
When you do something like that, you're pretty much asking for the GM to throw something at us. And he seems very willing to take you up on it. Might be better to just take it as read that we 'runners are normally alert, and let him decide when to call for perception checks...