I tried it last year (pre-DP/DR) for mild depression and I thought that it was effective but it might have been psychological in my case. I know that it's widely used for depression and some people are beginning to use it for anxiety as well. I started it when my DP/DR kicked in but didn't notice any improvement and discontinued it. I do however know that it takes about 2 months to notice its effects.
I was brought up in a hippie household so I'm prone to choose herbal remedies rather than "typical" medicine but I'm not sure that I'd use St. John's for anxiety. Are you using it for anxiety or depression? Have you ever read anything by Dr. Weil? This is what he says about St. John's Wart:
"St. John's wort. St. John's wort is an herbal remedy that has long been used in Europe as a treatment for mood disorders. Standardized extracts have shown an effectiveness equaling Prozac in the treatment of mild to moderate forms of depression. It should not be taken with anti-retroviral medications, birth control pills, or antidepressant medications, especially SSRIs like Prozac or Celexa. Try 300mg of an extract standardized to 0.3 percent hypericin, three times a day. It?s full effect will be felt in about eight weeks. "