During a registration process what would the reasons be for using: username/password or email/password combinations to register the user?


Is it a case of identification once in the system (may be preferable
to refer to a user by their username instead of their email)
Simplicity - using email means the user dont have to create two
memorable items?


What other reasons are there for choosing either option? Is there a relationship between the type of service? 


Question: Etiquette for posting civil and informative comments
Answer: What tone should I strike in comments?

The tone should be the similar to the tone you would strike toward a relatively new co-worker who stopped by your desk with a similar question.  You shouldn't assume "tribal knowledge" about how SO works, or what type of questions we like to see here.  The goal should be to help the questioner improve this and future questions.  Your comments should be ordered toward getting the information necessary to help the questioner solve his/her problem.

What are some examples of bad comments and their better replacements?

In my mind, this is the wrong question.  For many "bad comments," it would most likely be better to not comment at all, and simply use the voting and moderation tools.

Ultimately, the answer isn't some sort of awk or perl script that will turn a rude comment into a constructive comment, but to change our attitudes from dealing with questions as efficiently as possible to dealing with human beings with questions.

The only thing more frustrating than a rude comment is a "polite" comment given through gritted teeth, or belied by every other aspect of the person's behavior.  A 30 minute hold time is not soothed by the recorded reminder that "your call is very important to us" every 20 seconds.

The challenge isn't about how to fake civility, it's to actually be civil.  To consider the questioner or answerer to be an actual human person with an actual problem rather than one more thing we have to deal with today.

If this is too high a bar for you to clear in responding, then maybe it's best for you to take this pitch and leave it for somebody else.

Having said that, there is some validity to "fake it until you make it."  That by going through the motions of active listening, civil phrasing, etc., that we can become more genuinely compassionate to others, and the other answers offer some tools to help us do that.  It's just important to remember that moving to more civil wording is a step in the journey, not the destination.

It's also the case that human relationships include snark and flashes of anger, and this includes SO.  But hopefully, this is not the exception rather than the rule.