Many are asking these questions. Christianity Today suggests there have been many projects where unbelievers examine us. Take a look at one such story. If you know of other such stories, please, let me know.
However, the question I ask myself is "Who is receiving more?" My outlook on serving others has change dramatically over the last several years. I use to dread it. A feeling of panic would explode in my stomach. But that's because my heart wasn't there. I had no relationship and wanted none with those I "served". It's different now. I'm the one who benefits from the time I spend with those in the projects. Granted, I don't know many and it's still tough starting those friendships, but at least I know what's on the other side now. I know that I need them. Maybe that's why Christ promised "you will always have the poor with you." (Mark 14:1-11) Remember, sacrifice is key, and yet once done, it no longer is a sacrifice because you are the one to receive charity's reward.
Links:
http://blog.christianitytoday
http://drewmarshall.ca/blog