Oh yes. It was one of my formative childhood experiences. My first mud was Alter Aeon, but I haven't played in almost 10 years. I enjoyed myself during the 5 years or so that I played and got to know a lot of people. The first first thing I ever programmed was a bot to automatically heal group members.
Then Empire Mud, but I left due to disagreements with the admin. I loved the concept but it didn't really have the playerbase to support it.
More recently, I was on Procedural Realms. But I was affected by 3 separate instances of data corruption / loss, the last of which resulted in an unplanned pwipe since there were no offsite backups and the drive on the server failed. Years of progress gone due to lack of backups, so I'm never going back.
Ever since, I've been trying to find something else. Perhaps I'm just getting older but I don't have the patience to grind that I once had, which rules out most hack and slash muds. These days, I prefer something with interesting quests, places to explore and mechanics.
What muds do you play?