Possible Duplicates:
What is the correct way to pluralize an acronym?
What is the proper way to indicate possession when using an abbreviation such as Dr.?
An example:
Most DD's have good packaging skills.
How did things come to that instead of:
Most DDs have good packaging skills.
Compare that to:
Most Debian Developers have good packaging skills.
[update] This question was asked with the presumption that the first example is correct, so I was surprised to find that it isn't the case.