• Revaluations should be done annually, not every four years.  One reason for this are that you are more likely to get an accurate reflection of a property's current value, and not a value skewed by a housing market that was hot three years earlier and is significantly cooler now.  Another is that you spread the tax gains (and pain) over time, which is better for both the government and the taxpayer.
• But given that the county is doing revaluations every four years they should at least come up with a formula that weighs the change in the marketplace.  My understanding is that they are taking the average home sales for a certain area over a set amount of time, which I believe is the five year assessment period.  If your neighborhood had 200 home sales in the first 3 years of the assesment period and home prices were rising, but then only had 50 home sales over the last year of the assessment period while home prices were falling then the average would skew to the higher prices of a rising housing market that no longer exists.  That means your home value will not accurately reflect its current value in the home valuation, but rather an average of its value over the five year period.  What makes that inherently unfair is that you will be stuck with that higher valuation for five years, even if the value continues to decline.

The potential saving grace of the process is that the county commissioners determine our tax rate so they can lower the tax rate in order to lower the tax burden of higher property valuations.  Still, since most people don't trust politicians this is small comfort to most.  

Another point: when the property valuations are low at the beginning of the valuation period and then there's a sharp increase in the property values the county actually misses an opportunity to capture that increase in terms of tax revenue.  If we moved to an annual revaluation they could capture those increases in real time and even if the commissioners lowered the tax rate they would most likely still see an increase in tax revenue, but they would probably have fewer complaints from homeowners because the revaluations would more accurately reflect current values and would thus seem more reasonable.  Also, instead of seeing large changes in value from one revaluation to the next we'd see gradual changes that are easier to swallow.