I view it as a form of bribery - and bribery can be useful and effective. So I buy a couple boxes of cookies from someone I think can be worthwhile, then generously share them with my co-workers. If the janitor wants to sell me some lottery ticket for his church, that's fine too. Later - a few weeks or so - I'll ask the person for a small favor. This creates a channel of exchanged assistance. And if they consistently don't respond, I buy the stuff from someone else.
United Way is even easier. If you can't get away with giving them a buck, sign up for a full "fair share" through payroll deduction. Then quietly go to payroll and cancel it before it starts.
The neighborhood is tougher. I just don't bother to answer the door. (Grin!)
Everyone who knows me knows one important fact about me. I am outspoken politically. I will NEVER give money to United Way ever again because of their stand against the boy scouts. I tell everyone who wants my money exactly why I am not giving money to that org. I buy popcorn from the BSA and cookies from the GSA. If someone has those huge candy bars at work and I am starving for comfort food after a bad morning, I will pony up the dollar. But that is all.
I have never gotten involved in fundraising with my children simply because I am uncomfortable hitting up friends and co-workers for money. Like was mentioned earlier, I will buy something myself, but other than that, the younguns are on their own if they want to shill the coupon books.