Both my sisters saved theirs in my mom's huge chest freezer, since they both moved a fair amount during their first years of marriage.
The first sister to get married had their cake made by her former girl scout leader who's a semi-pro cake baker, and we're pretty sure it was a boxed mix (white and chocolate marbled, I believe). It got wrapped in (lots and lots of) layers of plastic wrap and foil and did okay. They said it was edible but not fantastic, which is what I would expect from frozen boxed cake.
My youngest sister got married in May of 2014, so their cake is still in the freezer and I'm sort of nervous about it, since I was the one that wrapped it for her - my grandma got sick a few days after the wedding so my mom flew out to be with her for almost a month and a half, so a lot of the final clean-up tasks kind of fell to me, since we didn't know how long mom would be gone. Her cake came from a local grocery store, so it's slightly denser, but probably won't have frozen much better than the other one.
I wonder if the use of fondant would help preserve frozen cakes any, since it seems like it would do a better job sealing in the moisture than standard buttercream. (I'm a fondant peeler when I eat cake, though, so I would just peel it off after freezing/thawing). No chance for testing that theory here, since both my sisters hate fondant.
I did have a huge dense chocolate-espresso cake I baked for fun and I froze most of it because I couldn't eat it all myself. It actually did beautifully in the freezer. I think part of why it did so well was the dense texture, and the fact that I wrapped each slice separately, so they froze and thawed more quickly. When I wanted a slice, I would microwave it to thaw and warm it up. It started to melt the frosting, so it wasn't very pretty, but it tasted good because it was warm. Because of that, I'm wondering if individually wrapped slices of wedding cake would do better than a whole tier too.