Any person with substantial British ancestry probably has a Smith somewhere in the family tree. In my own tree it's my 6th great grandmother, Martha (Smith) Kingsbury (1710-1771) of Norwich, Connecticut. No English surname really compares to Smith in terms of frequency. In the United States Smith is still by far the most common surname occurring 2,376,206 times in the 2000 census, outstripping the next most common surname, Johnson, by more than 500,000 (Census Bureau website).
The name Smith is an occupational surname for people who originally worked with metal, such as blacksmiths, tinsmiths, etc. Although it is not entirely clear to me why this particular occupation would be so widely adopted as a surname, it is clear that it has. Not only is the surname exceedingly common in the English-speaking world, but surnames derived from metal-working professions are among the most common surnames across Europe, including the surnames Schmidt in Germany, Ferrari in Italy, Kowalski in Poland, Lefebvre/Lefèvre in France, De Smet in Belgium, Kovács in Hungary and several others. The main exceptions are places where surnames are mainly derived from patronymics such as Scandinavia and Spain (for earlier posts dealing with patronymics click here and here).
For the month of March, I am going to do a series of Surname Saturday posts on names in my own family that are related to or have similar origins to the name Smith.