Sefirat ha'omer is about counting 49 days (7 weeks) from Pesach to Shavuot. In fact, this count defines Shavuot (which has no calendar date in the Torah). This is the primary purpose of the omer. Any other meanings or observances should enhance this purpose, or at least not detract from it.
The biblical Shavuot is an agricultural festival at the time of the wheat harvest. We count 7 weeks from the offering of the omer, the unleavened sheaf of barley, on the 2nd day of Pesach, to the sh'tei halechem, the two loaves of leavened bread on Shavuot (Leviticus 23:17). Even though eating matzah is unusual for us today (most of us eat it only one week a year), almost all grain-offerings in the Temple were matzah (unleavened), and chametz was the exception to the rule. The sh'tei halechem on Shavuot were the only communal offering of the year that was chametz. (The only other chametz offering was part of the todah, the individual thanksgiving offering. Thus the sh'tei halechem might be seen as a communal todah.) The journey from Pesach to Shavuot is a journey from matzah to chametz, from clearing all the chametz out of ourselves and eating only the austere bread of affliction to letting chametz back into our lives and eating the rich bread of thanksgiving. (L'mah hadavar domeh? Chametz, leaven, is literally microorganisms. When one takes antibiotics, it kills off both the harmful bacteria that cause disease and the helpful ones in the digestive tract. Therefore, after all the bacteria are killed off, patients are advised to eat yogurt, to reintroduce the good kind of bacteria into the digestive system.)
The rabbinic Shavuot is, of course, z'man matan torateinu, the time of the giving of our Torah. Thus, the 7-week journey is about the transition from freedom to responsibility, so that we can fulfill the second half of "Shalach et ami v'ya'avduni", "Let My people go so that they may serve me". Shavuot is the completion of Pesach, the atzeret at the end of it (parallel to Shemini Atzeret at the end of Sukkot), the ultimate purpose for which we are freed from slavery.
We count each day between Pesach and Shavuot so that we can be continually conscious of this journey from matzah to chametz, from freedom to responsibility. The omer is thus a serious time, but not in a mournful way (just as Yom Kippur is serious, but the happiest day of the year).
I'm a fan of the custom of studying a chapter of Pirkei Avot on each of the six Shabbat afternoons between the end of Pesach and Shavuot. The omer is a time for reflection on ethical behavior and on what it truly means to receive Torah. Thus the journey from "Moses received Torah from Sinai" to "What is the correct path that a person should choose?" to "Look at three things and you will not fall into sin" to "Who is wise? One who learns from all people" to "The world was created with ten utterances" to "All who engage in Torah" helps to guide these personal reflections and focus us as we head toward Shavuot.
With this whole framework in place, the idea of observing sefirat ha'omer as a period of mourning for Rabbi Akiva's students seems to come totally out of left field. Why are they entitled to 7 weeks of our time (or 33 days, depending on how you count) every year? Yes, I've heard that it's really about the Crusades, but the Crusaders or the Romans don't get to take over our sacred calendar, just as the Warsaw Ghetto Uprising doesn't get to take over Pesach. There is nothing about the omer period (as discussed above) that should make it a time of mourning.
I can understand the idea of not scheduling weddings during the omer, and that isn't dependent on it being a period of mourning -- we also don't schedule weddings during Chol Hamo'ed Sukkot or Pesach, which are clearly festive times. But most people get married a maximum of once in a given year, so all this means is scheduling the wedding for one time instead of another time. Refraining from listening to music for 7 weeks (or 33 days), on the other hand, is disproportionate to the importance that mourning Rabbi Akiva's students should have (if any!), and is inappropriate to marking the journey from Pesach to Shavuot.
Therefore, I don't observe Lag Ba'omer, because this cessation of mourning customs only makes sense within the paradigm of observing the omer as a time of mourning in the first place (which I don't do either). Lag Ba'omer also creates a false climax to sefirat ha'omer (I've heard people say things like "sefirah's over now"); the one and only climax of sefirat ha'omer should be Shavuot.
And let's not even get started on the idolatry surrounding R. Shimon bar Yochai. And no, I'm not shaving or cutting my hair tonight (though I will shave, as usual, for Shave-uot).
I guess the kabbalistic understanding of the omer (tiferet sheb'netzach and all that) is harmless and whatever floats your boat, but I think this is also a distraction. Case in point: I saw an omer calendar that had a suggested activity for each day related to that day's sefirot. The activity for the 6th day of the omer was "Create something constructive" or "Construct something creative" or something like that. What's the problem? The 6th day of the omer, this year and every year, is the 7th day of Pesach, when creative labor is forbidden! Oops! That's what happens when you try to overlay something onto the omer without regard to Pesach and Shavuot.
Today was the 32nd day of the omer; soon it will be time to count!
Next in the series: Why I don't observe the 2nd day of Shavuot.