This certainly isn't a great reason to avoid perennial calendars, but I honestly very much like that anniversaries fall on different days of the week each year. As a child a 'weekend' birthday gave me something to look forward to for multiple years to be able to party like Elton John or the Bay City Rollers. With a perennial calendar, if I were born on a dull workday, I'd be stuck celebrating in the middle of the school or work week for life! "No, cindy, I don't want to celebrate with the rest of the staff in the kitchenette with any more of your muffins."