Ok, a quick and not real elegant way,
Open a new column next to column B
and in your new Column C, enter the formula:
If a cell has a formula, it will remain blank
if a cell has actual text, it will display the text, in your case the word "yes"
Do a =COUNTIF(C1:C30000,"yes")
See how that works.
No, that's not going to work either, your going to need some VBA to get it to work.
Sorry my VBA skills are minimal at best.