Growing up in the Reformed tradition, we did not observe the season of Lent. As with crucifixes, vestments, and other traditions within the Christian church, Lent was simply 'too Catholic' to be observed within our circles. At first blush, I suppose such an objection may seem valid, but it really won't hold up to any scrutiny, especially if we, like many, reject Lent but accept Christmas as a valid Christian observance.
Am I overstating my case? I don't think so. Here's why...
First, considering history. I am not aware of any scholars or writers who would deny the impossibility of accurately determining the exact date (day/month) of Christ's birth from Scripture. The oldest dates for the observance of Jesus' birth appear to be in the Spring, only changing to December, in the West, under the rule of Constantine during the mid-fourth century. The first 'hard evidence' for the observation of Christmas on December 25th comes from a Roman calendar called the "Chronography of 354," dated AD 354. Prior to the legalization of Christianity under Constantine, any celebration of Christmas as a church holiday was at best sporadic (cf. Clement of Alexandria) but, more commonly, not mentioned (cf. Tertullian) or simply rejected outright as a pagan notion (cf. Origen [mid-3rd cent] and Arnobius[early 4th cent]). In short, the celebration of Christmas was not widely observed until the mid-fourth century.
In contrast, the history of the observation of a period of fasting, repentance, and preparation prior to the celebration of the resurrection (i.e., Easter) is much older than the history of Christmas. In the late 2nd century, Irenaus of Lyons wrote of just such a season, though it was not the 40 day season we observe today. His mention of what we now call Lent is not a remote example. Tertullian, who failed to mention any celebration of Christmas, wrote of a forty day period of fasting similar to what we now observe, though even here there seems to be widespread variation on the exact length of the time of preparation. There was such a wide variation in tradition, in fact, that the Council of Nicea (AD 325) expressly mentioned forty days as the suitable practice for this pre-Easter observance. Unlike Christmas, a Lenten-like period of preparation was so widespread in the early church that the Council felt it necessary to weigh in on the discussion.
From a purely historical perspective, then, Lent predates Christmas as a widely observed church season.
Second, considering theology. Any celebration of Christmas at all as a Church holy day (holiday) comes solely from tradition, as there is no express biblical warrant, command, or example. I mention this point only in response to those who reject Lent and other Christian traditions because they 'aren't in the Bible' or should not be considered permissible under the Regulative Principle of Worship. Quite honestly, you cannot have it both ways, rejecting one tradition over another on what I would argue are purely subjective grounds. To reject one and retain another is inconsistent.
So, if you do not observe Lent, why not? I'm not trying to suggest that Christians must, but I'm also poking a little at those who suggest that Christians may not. I should think we would all benefit from a deliberate season of preparation for Easter--reflecting upon our own sins/need for a Savior as well as preparing ourselves to be of further service to our merciful God.