It is most common amongst Jews. They do it because they consider it improper to write the name of God (though presumably God is clever enough to work out that they mean Him nonetheless).
je--s enough already. thanks for your answers all very god, er , i mean good. I suppose avoiding offending a non-existent amorphous er, thingy compensates for killing laods of people.
Its usually by Jews and people who show respect to Him - it shows reverence for the Lord.
BTW did you know that G-d's REAL name is never mentioned by Jews. Apparently G-d's real name was only said once a year by the highest priest... from that came the tradition of not completing or saying G-d's real name which in Hebrew is holy, but is transliterated in english as J***** as in J*****'s witness... . It's apparently a HUGE sin to say G-d's REAL name in vain.
The name G-D comes from the English word good. But G-d's name is not "G-d"...thats what we simply refer to Him.