I don't personally think that the Sabbath or "Lord's Day" is a question of liberty, even though sincere believers differ in their views and convictions about it. When I look at Rom. 14 and 1Cor. 8-10 (which I just finished preaching through), I find issues that are clearly acceptable. That is, the issues Paul describes under Christian Liberty are things that Christians undoubtedly are free to do, but some still have a weak conscience about. When it comes to the Sabbath issue, it's a matter of different biblical interpretation - a theological difference. I would say that, in order for it to be a matter of liberty, it has to be something that is clearly allowed - something that is neutral in and of itself.
I think we are too quick to lump everything that Christians disagree about into the context of "liberty". We can honestly disagree about the Sabbath, but that disagreement falls in a different category than whether 1st Century Christians could eat meat or whether a Christian can have a glass of wine.

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Mike Shingler
Pastor: Steep Hollow Baptist Church (SBC)
Bryan, TX