The Million Dollar Question:

"How much is my home worth?"
The answer to that question is "it depends". Not very satisfying is it. There are several ways real estate can be valued. The two most common methods are present value and market value, and depends on what the valuation is going to be used for. Both methods tend to interact with each other, and many people will confuse the two. Present value compares what similar properties with similar amenities have already sold for in the last 6 months. This method is the most heavily weighted with lenders and, sometimes, isn't as high as many people would think. The major problem with this method is that there may not have been any similar properties sold in the last 6 months in slower market areas; therefore an appraiser will have problems proving values to anyone.
A market value appraisal is what your local real estate agent tries to come up with. This is commonly offered as a Comparative Market Analysis of the value. In other words, what could the property actually sell for when it is properly marketed? In this method, not only does the appraiser look at what has sold before, but what is currently offered for sale. In a declining market (something we seldom see here in the Bay Area), this comparison to current competing properties is a sword that can cut both ways. Homes offered for sale for less than what has sold before will yield a lower market value (a declining market).
A real world example of market value would be "if that 2000 square feet, 3 bed and 2 bath on 2 acres sold for 'X' dollars, and smaller houses on smaller lots are listed for more then “X”, then this 2100 square feet on 2 1/2 acres should sell for 'Y' dollars". Using the same example for present value, the 2 homes would be valued pretty close to the same price with some minor adjustments.
So, unless you're going to sell, your property's value is based off what has already sold before, not what you hope to sell for if you decided to sell.

Conforming interest rates for fixed rate mortgages (under $417,000) as of 4/24/07 (a.m.) are
Rates quoted are for 0 point loans, for a quarter point reduction in rate, add 1 point.
30 year fixed: 6.125% (APR 6.188%) payments are $2,533.74/mo.
15 year fixed: 5.875% (APR 5.980%) payments are 3,490.78/mo.