It's something believers do.
I don't use the damn word, it's too slippery. I was reminded that in some
other languages there is a distinction made by having verbs whose
meanings add the 'in' or 'that' to the 'believe', and I seem to recall
being taught that distinction for English in school, and even instructed
to use these modifiers.
Since 'believers' believe _in_ the supernatural (that which cannot be
shown to be), and the simple 'believe that' is common for statements like
'I believe that my friend is a loyal husband', then leaving these
modifiers out is a gruesome mistake. (Although many women take the latter
statement entirely on faith and others just don't believe it....)
My take is similar to the E-Prime nuts, except of course I ain't a nut- I
don't use the word, and go out of my way not to. I can recommend this,
especially for atheists in the midst of arguments... but I won't go so
far as to urge it in any way. It works for me, both to get the point
across to another, and to clear my own vocabulary of slipshod words.