I've been doing this for about 3 years now and not once have I found myself regretting it or unable to afford anything that I want.
I was originally inspired by some Muslim co-workers who told me about the compulsory charity that Islam prescribes for them, and the voluntary charity that they then make on top of it. 2.5% is compulsory for all Muslims, and then most top up to 10% as the voluntary portion is their way to give what God gave to them and by doing so show appreciation for what they have. This happens regardless of how much or little people earn.
Now, I am not religious by any definition, but I was embarrassed and ashamed at how most of my friends and especially myself were not really giving much at all. And I also felt that I could also appreciate what I have by giving some of it away.
Somewhere in an Orwell book I recall reading a bit where Orwell tried to tip a taxi driver a large amount. The taxi driver refused, "I will still be poor tomorrow". That 10%, I don't need it... that alone isn't the definition of rich that I use. Even a bonus once a year won't make me as happy as just working on things I am interested in. So it seems clear to me that I have more to gain by helping others less fortunate with those things than I do.