Konnichi ha means "Good day" whereas Konnichi wa means "Good Afternoon", so on a forum like this where people could see the message at anytime of the day the former would be more appropiate.
Update: also the last character in Konnichi "wa" (こんにちは) is は which is actually the hiragana character for ha. :)
"Cogito cogito ergo cogito sum - I think that I think, therefore I think that I am." Ambrose Bierce