A nice man with one eye (I think he helps out at the bike station) on a bike stopped to help me on the canal when I had a flat and had broken my cheapo-s**t tyre levers by trying to get my cheapo-s**t tyres off my cheapo-s**t rims. Going as far as turning his bike round, cycling home to get his own tyre levers, and the returning to help me and give me a full lesson in flat fixing and tyre installation (such as the all important making sure the valve is lined up with the logo on the tyre!) all for free. He sold me TBS wonderfully and I made sure they got my old bike as a donation when it was no longer needed.
Anyway, back OT, ever since then I've been in the "at least stop and offer help anyone in cycling-related distress" camp. Most will say thanks and wave you on, but occasionally I've been able to help someone who quite obviously had no idea what to do.
I've found kindness breeds kindness in my limited experience - I dropped a wallet in Camden Town tube station and by the time I got home from London I had a postcard from London Underground asking me to call them up so they could post it to me (with all my Scottish money still in it!). 2 weeks later I found a money pouch with £70 in it on my street so I repayed the compliment and handed it in to L&B at St Leonards -I waived my legal entitlement to 15% finders fee when it was reclaimed.
I'm a bit more wary about the sort of kindness outlined above about dealing with the bucky/meths-drunk members of society, as I've been on the recieving end of their irrational violence previously when I found myself inbetween "them" and a female friend walking home one night.