Should a True/False value be a dimension

Should a true/false attribute be in the Fact table or a Dimension?

It depends...
If it is logically related to other attributes then it should be in the same Dim as those attributes
If you have a number of unrelated flags then consider putting them in a Junk dimension
If this is a standalone attribute then put it on your fact table as a degenerate dim

I concur, but I wouldn't put it on the fact, even if it was a standalone attribute. I'd create a junk dimension from the get-go, because it will be easier to extend gracefully in future and experience says you'll probably find more of the same later.
If it was on the fact, I wouldn't call it a degenerate dimension, by the way- that term tends to be reserved for the types of dimension key that don't warrant other descriptive attributes, like invoice numbers.

Do you count the number of times something is true or false? If yes, fact.