Sometimes we observe it, sometimes we don't. A quick search of our archives shows we've posted on the holiday every year since 2008, but not before that. Here's an interesting set o' facts about the holiday, from the Usual Source o' Facts as I know it:
Overall, in 2007, 33% of employers gave employees the day off, a 2% increase over the previous year. There was little difference in observance by large and small employers: 33% for firms with over 1,000 employees; and, 32% for firms with under 1,000 employees. The observance is most popular among nonprofit organizations and least popular among factories and manufacturers. The reasons for this have varied, ranging from the recent addition of the holiday, to its occurrence just two weeks after the week between Christmas and New Year's Day, when many businesses are closed for part or sometimes all of the week. Additionally, many schools and places of higher education are closed for classes; others remain open but may hold seminars or celebrations of King's message. Some factories and manufacturers used MLK Day as a floating or movable holiday. Many business that used to close on Presidents' Day now stay open on that day and close on MLK Day instead.*I don't believe I ever got MLK Day off while I was working. I certainly didn't get the day off while I was in the military because the Feds didn't observe MLK Day as a holiday until 1986 (I retired in 1985). Neither one of my civilian employers recognized the holiday, either. So, chances are you work for the gub'mint in one way or another if you have the day off today. The rest o' you should quit goofing off and get back to work.
*I removed a lot o' the links in the above paragraph.