Long story short, pretty much what the title says.
Obligatory wiki-links, IUC:
http://en.wiktionary.org/wiki/irregardless
Irregardless - Wikipedia
No.
It is not a word and is best replaced with **immaterial ** or **regardless ** depending on context.
No.
Well, sure it is. Many people use it; therefore, it’s a word.
Now, is it a “standard” or accepted word? That’s a whole different debate (and I don’t believe a general question). My guess is that it’s going to eventually become like the flammable / inflammable pairing and that irregardless / regardless will become accepted words with the same meaning.
Yes. Not in question.
Those links as well as Merriam-Webster all agree that it is non-standard, though.
But that’s not what you were asking.
It might be a word but what’s is supposed to mean? The meaning of ‘regardless’ is clear, as is the meaning of ‘irrespective’. ‘Irregardless’ is a double negative all on its own.
Can we ditch this concept of a word being “real” or not? A word is, citing Merriam-Webster’s very own definition, (the first to be listed):
Main Entry: word
Pronunciation: 'w&rd
Function: noun
1 a : something that is said
I just said “irregardless” quietly to myself. Ergo, it’s a word. Now as others have pointed out, a better description may be that it’s a non-standard word, as its etymology may well stem from misunderstanding use of the words “regardless” and “irrespective” (as you point out yourself with your links). For this reason, I would personally never use it.
So to summarize - word? Yes. Tacky hick’s word? Yeah, I think so.
Of course it’s a word. It’s a silly word, in my opinion, but nevertheless a word that many people use and whose meaning is perfectly clear.
Well, that’s arguable. As was pointed out by jabiru, it’s a double negative and therefore it’s a very messy, ugly, and potentially ambiguous word.
and besides, “disirregardless” is much betterer and has improved truthiness.
People use it. It’s a word.
Any more questions?
It’s a substandard colloquial usage, generally used as an intensifier for “regardless.” It’s considered a solecism in writing or careful speech.
When the Erie Canal was a big deal, there was a dedicated security outfit. They were disbanded long ago, and we are all Erie Guardless. 
Quote from The American Heritage Dictionary:
ir·re·gard·less adv. Non-Standard. Regardless. [Perhaps from ir(respective) + regardless.]
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USAGE NOTE: The label Non-Standard does only approximate justice to the status of irregardless. More precisely, it is a form that many people mistakenly believe to be a correct usage in formal style but that in fact has no legitimate antecedents in either standard or nonstandard varieties. (The word was likely coined from a blend of irrespective and regardless.) Perhaps this is why critics have sometimes insisted that there is “no such word” as irregardless, a charge they would not think of leveling at a bona fide nonstandard word such as ain’t, which has an ancient genealogy.
Only if you think too hard about it. Language doesn’t follow rules of logic. If you somebody said it to you in conversation, it would be very clear that they meant “regardless”.
A very cromulent reply.
Oh, come on. I just said “alabamiskoo,” therefore it’s a word. “Irregardless” is not something anyone who wishes to be taken seriously should say.
True, but that wasn’t the question. It’s a word, an it’s a synonym for “regardless.” It is not a nonce word such as “alabaiskoo,” but one used by many people with an agreed upon meaning.
Currently it’s nonstandard, and it may remain that way, or it may become standard like “bus” or “mob.”
Don’t misunderestimate it.