I contend that it is not!
Irregardless is a word…all u had to do was look in the dictionary.
irre’gardless, a. and adv.
Chiefly N. Amer.
[Prob. blend of irrespective and regardless.]
In non-standard or humorous use: regardless.
1912 in WENTWORTH Amer. Dial. Dict. 1923 Lit. Digest 17 Feb. 76 Is there such a word as irregardless in the English language? 1934 in WEBSTER (labelled Erron. or Humorous, U.S.). 1938 I. KUHN Assigned to Adventure xxx. 310, I made a grand entrance and suffered immediate and complete obliteration, except on the pay-roll, which functioned automatically to present me with a three-figure cheque every week, ‘irregardless’, as Hollywood says. 1939 C. MORLEY Kitty Foyle xxvii. 267 But she can take things in her stride, irregardless what’s happened. 1955 Publ. Amer. Dial. Soc. XXIV. 19, I don’t think like other people do and irregardless of how much or how little dope would cost me [etc.]. 1970 Current Trends in Linguistics X. 590 She tells the pastor that he should please quit using the word ‘irregardless’ in his sermons as there is no such word. 1971 M. MCSHANE Man who left Well Enough iv. 96 The sun poured down on Purity irregardless of the fact that it received no welcome.
From the Oxford English Dictionary
I guess for Americans it is - not for Britons 
Irregardless originated in dialectal American speech in the early 20th century. Its fairly widespread use in speech called it to the attention of usage commentators as early as 1927. The most frequently repeated remark about it is that “there is no such word.” There is such a word, however. It is still used primarily in speech, although it can be found from time to time in edited prose. Its reputation has not risen over the years, and it is still a long way from general acceptance. Use regardless instead.
Source M-W online
If you want to listen to it:
http://www.m-w.com/cgi-bin/audio.pl?irrega01.wav=irregardless
Rule of thumb for writing, follow Strunk? and White.
Strunk and White, defenitely the way to go, quite a handy little book.
Strunk and White should be given to every child, the day they learn to read.
I wish I had been…
All that really matters is that the word is a legal scrabble word. IR+REGARDLESS is quite a bit of points. Or… IR+REGARD+LESS Whatever. If you don’t play scrabble, then you will never know the significance.