I would say this depends on where you ski, how you ski and what you are used to. I prefer my skis to be razor sharp. Part of the time it's actually needed, or better to say, >I< needed them like this to feel safe with $20.000 of photo equipment on my back, while lot of coaches and service guys go down same course a bit less controlled way with their "I don't remember when I touched my edges" skis. The other time, when I'm just skiing for fun (either it's between the gates on injected snow or on public slopes which are soft or icy), I just prefer them to be sharp. This means I'm using file at least once a week, more likely twice, which actually brings it close to every 2 to 3 days (plus at least diamond and ceramic after every single skiing). Thing is, you can shave of very little edge when you know how to do it and when you have right tools. And it actually helps if ski is well maintained. With my skis, I shave very little of edge away with file, while when dealing with friend skis, which they bring them to me once every few months, I file like crazy to get to at least somehow decent sharpness.
Another thing to consider is ski itself. As I wrote before, race skis have thinner edges by default. Skis I'm skiing have most of them edges filled away even further, as they were used (at least for test) by certain racer, so with my filing (and skis history) they normally survive one winter, but it's a bit easier for me, as "hey mister, I'm through the edge, can I pop for beer and pick new pair like today evening?" works for me :) With normal non-racing skis and their thicker edges, I wouldn't worry all that much about this, as you can file for long long time before you are through.
Can you expand a bit on what is involved with "ceramic"? The reason I ask is Falline Tuning and Repair at Sun Peaks has a ceramic edge sharpening machine that puts an incredibly shiny polished edge on a ski. Is there a way to do something similar by hand at home?