To me, it all comes down to who the friend really is to me. It doesn't matter who you are; surely, there are friends who helped you greatly in your time of need, no? And it is for those friends and those friends only that I would gladly risk my life for.
Don't get me wrong, if I could, I'd help strangers as best I can. It's just that, where I live (and I'm pretty sure it happens everywhere else), it's very, very (emphasis on very!) risky to simply help someone with car troubles or someone who's lost their way, simply because most of them are conmen.
So, for my friends, I'd give my life. For strangers, maybe not.