Ok, so this is turning into more than 3 cents. BTW I'm pulling a lot of this out of my ass, but most of it I found in various places around the web when I was researching my own fridge:
Temperature fluctuations continued: Basically it's about tradeoffs, is a wine fridge set to 55 degrees and fluctuating a couple degrees plus and minus over a 30minute-hour cycle better than your other options? Unless you can dig a cave under your house it probably is. And remember, even full room wine "cellars" use themostat-controlled air conditioning, so they're not immune to this "problem" either (although they're probably a little better).
Once cent on light: People who supposedly know what they're talking about say that wine, especially white wine, is suseptible to UV light. Common glass, even clear glass, blocks most UV light, but not all of it. The amount it blocks depends on the thickness of the glass and its makeup (darker glasses generally block more types of all light, including UV). It's possible that other wavelengths of light also affect wine. Ideally your fridge would NOT have a glass door. Unfortunately it seems fashionable for them to have glass doors; In fact, many are simply small fridges with glass doors. At the very worst, even with a clear glass door on your wine fridge, at least you have another layer of glass between your wine and the world.
One cent on vibration: Compressor-based wine fridges will vibrate. Specially designed fridges probably do a better job at isolating vibration from the compressor but i'm sure it depends on the model. On the plus side, compressor based fridges don't run constantly unless your fridge is in a hot place, and therefore don't vibrate constantly. I found it difficult to find any rationale as to why this amount of vibration was bad, but it seems that vibration can unsettle the particulate matter that otherwise would settle out of the wine. How much vibration is required to unsettle the particulate matter is, I think, a bit debateable. But what do I know. Similar to temperature fluctuations, I think the vibration that wine snobs are worried about are the vibrations from things like being shipped in a truck or being moved around by hand. If fridge vibrations were so bad, then things like walking around your house would screw up your wine ageing too. Heck, maybe it does. Whatever the truth, some vibration is probably worse than no vibration, and I think it's the Sub Zero people who said that like light and temperature it is another source of external energy that is going to affect how that wine ages. Again, however, it's a tradeoff: is the little bit of vibration from the fridge worse than leaving your wine out at room temperature? Probably not.
One cent on humidity: This is probably the least of the problems, but supposedly the corks can dry out in low humidity environments which will cause too much air to get past the cork, or worse, for the cork to crack. Too high of a humidity can cause (additional?) fungus to grow on the corks or, heaven forbid, for the labels to peel off (but if it doesn't have a pretty label, it won't taste as good!). Generally your wine fridge won't be too humid, but it could be too dry if you live in a dry climate or if you try to use a converted frost-free fridge/freezer. Most wine fridges use little water resovoirs that they just let evaporate into the fridge air and you have to keep them topped up. If yours doesn't have one you can get one from a cigar shop (people use them in humidors for the same purpose). If you're using a frost-free fridge/freezer I'm not sure that would be enough to keep the humidity up. Score one point for screw-topped/synthetic corked wine.
Like I said, this is what I could gather off the web when I was looking, anyone who knows better, please correct me.
I'm putting WD's kids through college.