I've been engaged for almost two years now, I'll get around to planning my wedding one of these days
I don't offer a free cake on the anniversary, I did think about it when I was setting things up. For me, I worried it would be more of a hassle-plus the added fee, time, etc.
I offer this option for my brides: a small cake, same flavor as one of the tiers, simply iced for the couple to enjoy on the evening of their wedding. I've already got the batter and the icing made, it's just something small that I recommend they have a family member add other goodies to their special box, (I copied this idea from Earlene-I believe she offers a 6" heart shaped cake that are all decorated the same with her lovely piping).