The Dallas appraisal district just sent out their 2009 Dallas tax assessments based on their most recent appraisals. How they come up with the appraised values is beyond me, but it's often not very accurate when compared to actual market data (known as comparable sales, or comps). I know that it's human nature to put credence in tax appraisals but don't be alarmed if they reduced the value of your home. Instead, enjoy the reduced taxes while you can, because it doesn't appear that Uncle Sam will be lowering ANYBODY'S taxes anytime soon the way they're blowing through taxpayer cash and newly printed money.
So don't sweat a low-ball tax assessment if you're selling, and don't put much value in a tax assessment of a home you're considering to purchase. Accurate market data will compare the red apples to actual red apples - not the sorta reddish apples, the yellow apples or the green ones.
Also, if you're curious about a tax assessment for a particular property, just visit http://dcad.org/