i tend to although i know i shouldn't. it really depends on how they're "asking" for money. the pathetic guy who just sits there with a sign, not bothering anyone tends to get something. if someone comes up and asks me for money, they're not getting anything. i don't know why, but that's my system.
have you ever had anyone get aggressive about asking for cash? i did at the walgreens on the corner of main and north in buffalo. some hardcore dude was hanging outside asking for money. i told him no, and started to walk back to my apartment. he started to follow me, screaming about how i was wearing nice clothes, (which wasn't really the case) so he was sure i had money on me. he started getting louder and louder and walking faster. just so happened that a cop car drove down the same street. the guy shut right up and turned around.
i've also gotten into it with someone who did gas can in the hand, i ran out about a mile down the road and need help. that was my fault though. i was such an !@#$ to him from the get go. in my defense, who still tries that nonsense anymore?