I think it's more important for us than for our kids-lol. My daughter cried the first day of kindergarten and it was very hard on me but she doesn't even remember it now and it was only a year ago! She ended up loving her teacher and loving school and she still feels that way.
I think the parents attitude toward school and toward the child makes more of an impact than the first day of school all by itself.
I do not remember anything about that day. In my case it probably means that it was a good day because the majority of my childhood memories is filled with stress, bad luck and many other negative things (i do have a few good memories but they are all tainted).
I don't think in the grand scheme of things that it really matters all that much. There may be certain things that stick out about that day, but I think unless something really memorable happened it doesn't too much impact the rest of your life.