Tis, a strange bowl of Split-P soup indeed. Normally, the distinction between the confessionally Reformed is just that confessional. Meaning the Continental Reformed (Primarily Dutch as we really don't have many Swiss or German Reformed Denominations anymore) follow as their summary of Scripture's teaching and secondary standard The Three Forms of Unity (Heidelberg Catechism, Belgic Confession and The Canons of Dort) and Presbyterians have the Westminster Confession of Faith and Larger and Shorter Catechisms. There are some differences but in the main, we are all one big 'somewhat' happy family.
Historically, the Continental Reformed (With the exception of Geneva) after the Reformation culled their adherence to the Liturgical Calendar down to what are known as the 5 Evangelical Feasts including only; Christmas, Good Friday, Easter, Ascension, and Pentecost. The Church in Scotland (Presbyterians) eliminated all but Lord's Day observances. So, the strictest amongst Presbyterians will not even celebrate Christmas or Easter. However, the only denomination that I am aware of that doesn't currently allow for liberty on this issue is the
Free Presbyterian Church of Scotland (not to be confused with the
Free Church of Scotland or the
Free Church of Scotland (Continuing) or the
Free Presbyterian Church of Ulter/US.)

In the FPCS denomination celebrating either would be an area for which one could/would be open for church discipline. Originally all Presbyterians believed this.
Today, in the conservative or Traditional denominations the observance varies. But none (other than FPCS) I am aware of make it a matter of discipline. As for my denomination we, have no special services, no decorations ect. Most likely the Pastor will just continue preaching through what ever book he has been preaching through, so basically there will be no corporate or public celebrations. (This would be to burden the conscience of a brother and be a breach of liberty.) But, people in their homes do what their conscience dictates. I have numerous picture-Christmas cards on my refrigerator from families in my congregation.
As for the PCUSA and the RCA well... what can I say both long ago, from our perspective, left the Reservation. (Yet, both still have "some" conservative Reformed pastors and congregations and internal organizations/groups that are trying to call them "back")
The difference between the Traditional R&Ps and the Mainline R&Ps is Grand Canyon-esque. But rest assured that what is now the PCUSA does not in the grand scheme of time have a long history of such observances, and while the RCA has a history of the 5 Evangelical Feasts, here you should note the conspicuous absence of Lent.
A good rule of thumb is that small R&P denoms are more likely to be more conservative, that is, in general to be discerned in the classic sense of "conserving' the ways of old; and large R&P denoms are not. Of course the PCUSA is hemorrhaging people and congregations as from the Carotid or pushing them out with the PSI of a Fire hose!
This is a link to an association of those that would be traditional (But certainly varying on many specifics)
http://www.naparc.org/
EDITED TO ADD:
For our a more International Flavor here is a International link to more conservative denoms ...
http://www.icrconline.com/members.html
The CRC -Christian Reformed Church- was a NAPARC member for a number of years but was
their membership was suspended a few years back.