Hiya, :)
Not something I've used, but two points come to mind :
My mate's Mum has used it for years to help with reactive, mild - and shorter term depressive episodes ; both as a curative and as a preventative . She claims it to be very effective for her, and is rational enough to have ruled out placebo effects e.t.c
Although 'mainstream' medicine do not seem to tout it ( at least in the U.K. ) I found it very interesting to note that if a person is taking (prescription ) M.A.O.I drugs, then St. John's Wort is cited as having enough of a chemical / Psycho-active action on neural pathways - as to make it dangerous to 'stack' with M.A.O.Is and certain S.S.R.I. drugs. What clouds the issue, is of course that the later warnings also apply ( to a lesser degree ) to other Herbal substances, like Ginko - and Ginseng.
I feel ( through experience but not intended as dogma ) - that if one is asking about the efficacy of 'over the counter' solutions - and /or attempting to Self medicate on such, then it's often better to discuss it with a health professional at the outset, even if the solution remains an informal one.
In B.K.P terms, I like to think of the visit to a General practitioner , as being the equivalent of " Wiring the pickup straight to the jack socket at the outset - to establish a solid foundation for further fault finding ". :)