Research is indicating that Cinnamon's effects on a diabetic vary depending on levels of insulin-resistance as well as other issues.
Cinnamon has been consistently shown to IMPROVE insulin-sensitivity, so if your blood sugar issues are related to insulin-sensitivity, then it will usually have an impact.
If your diabetes is a result of both impaired pancreatic function AND insulin-resistance, it may help somewhat, but not enough to register as a huge difference on your blood glucose records.
For me, I noticed an improvement in my BG numbers when I started cinnamon - but at the time I was still quite overweight and quite insulin-resistant. Now that I'm at a much healthier weight, it seems my insulin-resistance is much lower than it was, and the cinnamon has much less of an impact. (I found that out when I ran out of it, and went about 2 weeks before picking up more... the overall trend was that my BG only went up a few percentage points for the big picture...)
However, even if it only helps reduce my overall blood glucose levels by 3-5%, I'm more than willing to continue to take it. As I see it, if I can do three things that each offer a 3-5% improvement, that turns my 6.0 A1c into somewhere between a 5.1 and 5.5, which is my goal.
=)