How should we define tithing?

I came across this blog post "Giving Joyfully" via Shane Raynor's recommendation. The author, Jessica Miller Kelley, suggests that tithing does not have to go exclusively to one's religious community — that gifts to other charitable causes can be considered appropriate beneficiaries. It's an interesting concept, and I see the merit in it. At the same time, I know how churches struggle to pay the bills, and how disturbing this idea must be to those fighting to keep congregations afloat.

This brings to mind a prominent theme in the United Methodist Church today, that we are called to "extravagant giving,"  and what that means in a place and time where there are thousands of worthy causes unaffiliated with religion.

(There is plenty of information about this concept online and particularly in the writings of Rev. Robert Schnase and elsewhere online, but if you are looking for a quick introduction, try these links to a sermon introducing the idea and a list of scriptural sources upon which the idea is based.)

What I have read about extravagant giving is focused on giving to the church, but should the people of the church focus so specifically on church-sponsored efforts? Or should donations to other resources come from what one can give after the church's 10 percent is met?

In the interest of full disclosure, I have to admit that it's easier for me to voice these questions because I have so little in the way of monetary assets anyway as a full-time grad student. Still, it's an issue that I know I will deal with again in a more meaningful way, presuming that gainful employment at a living wage is awaiting me after graduation.

I'm interested in what you think. How do you allocate your giving to various causes and organizations, and how do you deal with these questions about how and to whom we should give?