I had planned to simply post the following:
Irregardless is not a word, regardless of what you hear. Don't use it.
Short, sweet, and to the point, right? But then I began to worry that "irregardless" has been misused so frequently that maybe it's now considered okay. (You know, like girls calling their friends "wifey"--if enough people do it, everyone thinks it's alright. I know I'm gettin' old, but there's just something not right about that.)
So you know me. I checked. And what I found is that most sources that acknowledge "irregardless" as a word (and there are many that do not) provide a caveat something to the tune of "improper usage" or "use regardless instead." Hooray!
And I also found out why. Wrap your mind around this brilliant reasoning: "Since the prefix ir- means 'not' (as it does with irrespective), and the suffix -less means 'without,' irregardless is a double negative" (Wikipedia). And everyone knows two negatives make a positive, which means that when people say "irregardless" they are actually saying the opposite of what they mean. Tee hee. I LOVE that.
So, irregardless of what you've heard (c'mon, you know I HAD to do that) use "regardless". It's the single negative choice of experts everywhere. (Thumbs up and big cheesy grin.)