Right, some theology.
If you know your Old Testament, you'll be aware that the practice if tithing is instituted while the Israelites are in the wilderness, having exited Egypt. They are told that a tenth of everything is to be 'holy to the LORD' (holy meaning 'set apart') and therefore given to the Levites, who are in charge of the Tent of Meeting and religious stuff generally. A tenth of that tenth is burned as an offering, with the remainder being for Temple upkeep, the priests' living costs, and alms for the poor.
This practice is continued throughout the Bible, and through the history of the Church.
Since we all pay tax to government – which functions in a very similar, distributive way as the Biblical tithe (paying for public buildings, public servants and 'alms') – is it appropriate to regard tithing to the Church as separate to taxation?
My thoughts (at present):
I think that the Biblical-era tithe did function, to all intents and purposes, in an identical manner to contemporary taxation. The difference being that tax is purely practical, not moral – the government doesn't tell us to pay our tax because of how it reminds us that all wealth belongs to God, and that in giving it we are releasing ourselves from bondage to it. That would be weird. Taxation fulfils the practical purpose of tithing, but doesn't express the underlying motive of God in instituting the practice in the first place. That's just not what He was getting at.
God doesn't need our 10%, we know that. We know that he's really after our hearts and that the actual issue of 'to tithe or not to tithe' is basically a red herring. The issue would be more obvious if the question was more like 'to be generous or not to be generous' or 'to put faith elsewhere but money, or not'. Therefore, I am not a fan of popping our 10% in the offering basket, or feeling guilty if we haven't.
[By the way, my view on this may well be coloured by the fact that, more often than not, churches prioritise their tithes-and-offerings money incredibly badly – something like 80% of Church income is spent on buildings, salaries, PA systems etc., while only 0.01% is spend on missions in the unreached world. Badly remembered statistics, but that's the gist.]
So, do we tithe or not? If I had an answer, it'd be something like 'yes, but differently'. I personally think that a lot of our dependence on 'ministers' would disappear if we stopped tithing to the Church (we might even end up with congregations of a more manageable, personal size too), but the real issue, I think, is do we give out of obligation – because the Bible says '10%' – or because it is good to be generous with all that we have. And once we've worked out our motives, we might then be free to realise that anywhere we give is good, because giving is good. We can give money to church, but we can give everywhere else too. We can give all that we own, or give our spare time, or give our prayers or our work or our company. That's generosity, I think. That's what God was getting at.