Yeah, the limits of expression of religion are boundless. When organizations such as Scientology become a recognized religion within United States, is it ever a wonder that some religious expression starts to conflict with other civil rights? Neither should take precedence in my opinion, but should be considered case-by-case. Of course if there is a law stating you must come to work, and then your religion demands you cannot go to work on this day of worship, then the religious expression should take precedence. But not all cases of expression can be clearly outlined, there's obvious ones like day of religious observance/worship, holidays, religious garments, etc. -- but baking a cake is not a fundamental right when it comes to religion.
I think the discussion has somewhat derailed from its focus -- we should not be talking about the rights of the lesbian couple & the legitimacy of marriage, but the rights of the baker. The rights of the lesbian couple, in my opinion, has nothing to do with the issue. It could have been a black couple, a hispanic couple, a muslim couple -- all of these are incidental traits, what is pertinent in this issue is whether or not the baker can withhold service to anyone based on any discriminating feature (a discriminating feature outlined by his respective religion). Christianity may have a problem with homosexuality, but it also has a problem with people of different faith and religion. This is very important, because if this case is ruled in favor of the baker, it will be a gateway case not only against lesbian couples, but all of the above. The Qu'ran specifically calls out Christians and Jews in its passages, from which you can argue muslim bakers might refrain service to them (refer to Sura 9:30, Quran).
As for my own stance on the situation, the individuals has rights as a Christian, but obligations as a baker. These two must be isolated from one another. Yes, he has the right to observe his own religion. But as a baker, he cannot withhold service without legitimate reason. Homosexuality, although problematic with christianity, is not a legitimate reason. As I mentioned in a previous post, Christianity labels homosexuality is a sin, as is murder, theft, lying, adultery, non-observance to the Sabbath, non-observance that there is only the christian God. As long as the bible does not explicitly say "Thou shalt not bake for homosexuals", this case is overreaching (in the sense that if homosexuality is enough grounds to withhold service, so is all the other sins, including no service to other religions; "Thou shalt have no other Gods before me"). In the realm of religion, you can withhold service to whoever you'd like (withholding lesbian marriage in your church). But in the realm of bakery, you cannot