Hmm, I've never seen that misuse of "defiantly". I often see definitely misspelled "definately" or "defanitely".
Pretty much my feeling as well. I haven't seen too many misuses of "defiantly" vs. "definitely"...but I certainly do see various misspellings of "definitely".
My opinion is:
- if you're e-mailing someone that you don't know well (coworkers, strangers, folks you may be involved with in a buy/sell process, etc.)
- as you develop a reputation & are a regular on an internet forum
...it's probably best to do your best when it comes to grammar, spelling, word usage.
Non-verbal communication (e-mails, forum posts, Facebook, etc.) is becoming (or has been) more & more prevalent...and bad habits developed & "practiced" everyday during electronic communications can sometimes inadvertently be used during more serious written/electronic communications.
It's kind of like burping, farting, or picking your nose...
"Stupid is as stupid does!"
- Nick