I am a degreed physicist that doesn't work in the field. (Just to show my age that was back in 1970) So I am familiar with metric measurements.  As for temperature, fuel, drinks, distances, what difference does it make?  Miles, feet, pounds, etc. are ingrained by usage, true.  But in the end what difference does it make to go 11 miles or ? kilometers to work or to grandmother's house, etc.  I know electrical measurements, and many other items are metric, but for football fileds, baseball diamonds, weights, etc. why change?  To me it is confusing to say something weighs a kilogram when I was taught that kilograms are a measure of mass, and that a kilogram is a kilgram no matter whether you are on the moon, Earth or Jupiter.  I don't really know if they are using a Kg for weight because no one over 40 will probably ever leave this planet.  But if you wat to get technical, that Kg of weight is not the same all over the Earth either, because of differences in gravitational acceleration.  Might not be significant, but it will be different. 

Sure, I don't know how many tsp in a Tsp or a cup, but I can look that up as well.  I do know how many ml in a L, but converting that to volume in cc is not consistent unless you are talking water.  Are we going to change our measure from sq. ft./sq. yd. to sq. m?  Carpeting or housing would work fine, but the wall studs are 8 foot, not 2.5 m or so, that will have to change when we go metric.. It might be easier to measure land in sq Km, in lieu of acres, because acres is not an easy measurement, sq miles is.  How about the layout of this country?  It is laid out on the sq. mile--most county roads are a mile apart in either direction (at least in the great plains states), city blocks are laid out in foot measure as well with approximately 15 blocks to the mile is that 13 or 14 blocks to the Km?  Who is going to re-measure all that just to make you happy?  Who will pay for it?

A lot has to be thought out before mass conversion.  Temperatures for the weather have no need to be in Celsius vs Fahrenhiet, why not go to degeres Kelvin  have everyone feeling hot at 273 deg K. when it is just 32 deg F, or 0 deg C,  inches of rain vs. cm, etc.  To us old fogeys that 0 is considered cold not just a cool 32 .  Why?  What difference does it make to spend so much money needlessly?  Just so some one can say we are consistent with other countries?

In the end it will cost lots of money to change all the road signs, someone has to convert those miles to Km or re-measure everything.  Money that can be spent elsewhere on more fruitful endeavors--like fixing bridges, or the roads themselves, than change for change sake.  Most medicines that have a dosage provide a small cup with the right dosage maked on them already.  Change all gasoline pumps to read Liters instead of gallons and to price per liter or get a 4 liter designation to make it feel the same, switching from $/gallon to Cents per liter would relly be confusing, all the tax rates would have to be changed.  Maybe we don't want to be a one world order.  It is true that the Imperial gallon is different than the US Gallon, and weights are different in other non-metric measures.  They are in the process of redefining all of the Metric System measures, too.  How will that affect the public? 

I hope I have corrected all my typing mistakes, and if not, at least my rant is readable.

I could not agree more.  So many measurements we use in everyday life are nominal or have such large tolerances that metric vs. traditional is meaningless.  Is a 2x4 going to become something different if we decide that it is now a 50x100 or a 38x88 or something else - none of which will be an actual accurate measurement of the wood's cross-sectional perimeter.  We certainly are not going to start using different sizes of wood that would then be impossible to retro-fit into existing structures.  Does it make a difference if we load a pick up with a cubic yard or a cubic meter of mulch?  In any case, the loader operator is still going only put as much in our truck as his loader bucket will hold.  It may be a yard and a half - it may only be half a yard.  Are owners of real property going to be better served if they now own a fractional hectare instead of a fractional acre?  Are county clerks, title agents and land surveyors going to be able to accurately convert all the property transfers into hectare units on the new recordings and who is going to bear the burden for the inevitable errors?

I use both measurement systems everyday.  All measurement systems are absolutely arbitrary and none are any more accurate than any others - provided that you use accurate or calibrated measuring devices.  You don't want to be like the guy who polished the Hubble's mirror and assumed (just because his data said so) he had exceeded the theoretical reflectivity of glass without going back and recalibrating his reflectometer.  Feet and inches are certainly must easier to estimate w/o a measuring device, and as a carpenter, it is much easier to think in terms of halves, quarters and thirty-seconds than it is to think in terms of tenths of anything.  Yes, it is easier to do calculations with decimal fractions and yes, it is easier to scale up and down a unit system that was designed as a unified system.  So what?  If you can't do fractions in your head, you aren't worried about measuring anything to begin with.  Likewise for simple memorization.  

In our lab we use metric for most liquid measures and most measures of mass less than a kilo.  Above a kilo we go to customary units and use balances calibrated in tenths of pounds.  Measurements of length are all decimal however the units used, SI or customary, are dependent upon the specification dimensions for the product.  There is absolutely no reason why both systems cannot coexist in their own spheres, nor is there any necessity why either should supplant the other where it would not be an improvement.