There's an old joke that goes like this:
One Shabbos morning, a fellow walks into a shul that he's never been in before. He finds that he likes the davening... the people don't talk too much, they're friendly, they sing all the tunes he's familiar with, and so on. The service goes on pretty much as he was familiar with... with one exception. Whenever anyone went up to the aron (Ark) to take out or put away the Torah, he would bow to the right. He was curious about this custom, but didn't say anything about this strange and heretofore-unheard-of custom for fear of making waves.
And so, a few weeks go by. He eventually gets p'shicha (the honor of taking out and putting back the Torah) and, not wanting to upset the people in his new shul, also bows to the right when taking out the Torah and putting it back after the reading. Finally, he can contain his curiosity no longer. After davening, he goes over to the gabbai of the shul and asks him about this curious custom of bowing to the right. "That's just the minhag (custom) here," the gabbai told him. "I don't know the origin of the custom." So, he asks a few other shul officials, including the rabbi. None of them can answer the question... all they know is that it's always been done that way. Finally, someone tells him to ask Shmuel. Shmuel is ninety years old, the oldest person in the shul. He's been with the congregation longer than anyone else who is currently alive. Certainly, he's told, if anyone knows the origin for this minhag, it would be Shmuel.
So with some trepidation, the man approaches Shmuel and asks him the question. Shmuel thinks long and hard, searching the dim recesses of his memory for that long-lost moment when they started this bowing to the right. Finally, after a few minutes, he says he's got it. "Fifty years ago, before we remodeled," he said, "there was a steam pipe coming out of the wall there. If you didn't bow to the right when you approached the aron, you got conked on the head."
I often wonder how much of what we do today, as Orthodox Jews, falls into the category of "Steam Pipe Judaism." By this I mean practices that began for ahalachic external reasons that are no longer applicable, although the custom remains with us. I would not be surprised to find that a fair amount of what we do has no actual halachic basis if you search back far enough.
Now, I know that the first example many of you are going to bring is that of Yom Tov Sheini Shel Galus (the second day of the holidays observed in the Diaspora). However, that doesn't fit the bill... there was a legitimate halachic reason to institute that. True, the reason for it no longer applies, as we now have a set calendar, but nonetheless, we chose to continue to observe the extra days.
What I'm looking for are things that had no halachic basis when they started, such as the bowing to the right in the joke. I don't know of any off the top of my head, but, as I said above, I wouldn't be surprised at all to find out that at least some of our practices fit this category. Anyone have any ideas?