Hi Wild_Swan,
From what I understand, Humira can take from 3-6 months to work. According to the Humira people, however, if it hasn't helped by 6 months, then it most likely won't be effective.
As for myself, I really had no idea if it was working or not (I'd been on it nearly 6 months at the time) until I had a colonoscopy and lo and behold the ulcerations were healed. Unfortunately, I had scar tissue in my terminal ileum and ileocecal valve. Thus, I had severe stricturing and had to have a small bowel resection. Humira can reduce inflammation and heal ulcerations, but does nothing for scar tissue.
Prior to my surgery on 7/30, I used Humira once every two weeks. (I'll start it up again soon). I also noticed that about 5 days or so before I was do for my next injection, I experienced more Crohn's symptoms.
Hope the Humira ends up working for you!