The Oxford English Dictionary sites the meaning as:
exclam a polite expression of gratitude. n an instance or means of expressing thanks.
Such a simple little phrase and yet we don't use it..
Why is this? Has it now become an 'implied' word?
I have been a member of this great forum for nearly 4 years now and one of the little things that irks me is when a member asks for advice, receives a plethora of helpful responses (sometimes 
) - yet sometimes the original poster never says 'thank you'.
It is free. It costs nothing and it makes respondants to a post feel that they've helped.
To those people who have helped me in the past - Thank you 
Sorry - Its Monday morning and I've had a bad nights sleep. I need coffee.