Tithing is a difference of opinion as to rather a person is an active Christian or not, and what church they go to.
I preach that tithing is 10%. That is 10% of our income and 10% of our time. They are not interchangable. I teach my church that one should not replace giving financially with serving more. Likewise, one should not neglect service by simply giving more. To be a member of my church people have to pledge their support of the church with the prayers, presence, gifts, and service.
A pastor once should a tought I enjoyed. His wife ahisd himself felt tithing his $8,000 income was easier when he was early in his career more so than his $80,000 income.
My wife and I have operated on a tithe first philosophy. We remove 10% from our income before we even budget, pay any bills, or really do anything. As far as we are concerned, if we don't tithe, we are stealing from God. After our tithe, we then figure out what we have and what we need. So far, we have always been more than blessed again and again.
Also, I believe and teach tithing is to the church alone (not all-inclusive charity giving). Biblically, tithing is not equatable with any charity giving, but specifically with support of the religious (Church) institution.
That said, I do not believe that it is an absolute issue. I preach that it must be progressive. I do not expect inactive Christians to tithe. If a person claims to be a Christian, but is not active in a faith community, I dont have the expectation that they will be giving 10%. If a family is giving 2%, I do not expect them to jump to 10%. I ask them to jump to 5%, the 7%, then 10%. If a person is giving 10%, I ask them to take the next step.
Bottom line though, we cannot and should not be legalistic about the nature of tithing. Tithing is a spiritual discipline that is reflective and supportive of our relationship with our Lord.
Side note: Studies have shown that tithing in this country from church going Christians hovers around 2.4%