The minimal, if any, effect that cinnamon had on me was trivial. Reducing my carb input by just a few grams had a much greater effect. I still use cinnamon as a spice frequently and infuse it in my morning coffee - but for taste, not BGs. It did affect my post-breakfast BG peak indirectly, because I no longer add milk to my morning coffee as a consequence.
I use many other herbs and spices in my menu. Some for taste, some for medicinal purposes, some for both. Some have proven benefits, such as turmeric for some cancers, some are anecdotal. My attitude is that if it is not harmful I have nothing to lose and a possible gain by adding such things to my menu. However, I do NOT buy capsules or pills of cinnamon, or turmeric, or garlic or anything. I eat them by including the herbs, spices and specific foods regularly in my normal way of eating. Sometimes by spicing up an existing recipe, such as a sprinkle of turmeric and black pepper (the two are complementary) in a morning omelette; sometimes by adding new spicy dishes to my menu, such as Asian stir-fries etc.
So I have tiny amounts of many things almost every day.
As I wrote this I started reviewing the herbs and spices in my menu over the last few days. Just normal days, nothing unusual. Turmeric, cinnamon, nutmeg, grated black pepper, cumin, paprika, thyme, mint, basil, rosemary, hot chili, fresh garlic, grated ginger and the broad combination spices of garam masala and commercial curry powder. That's in addition to ensuring my menu also included items like avocado, nuts, psyllium husks, leafy greens, onions, capsicum (peppers) etc. And, of course, a modicum of red wine. Most of my herbs are grown fresh at home. When the crop is over-abundant I dry it, chop it and store it for future use out of season.
As to which of those, if any, is helping my diabetes or CLL, who knows. But I'll follow my docs' advice and keep doing what I'm doing.
Because, even if they don't improve my health, they definitely help a slightly restricted menu taste good.
Post-script, 18th February 2009
I just became aware of this paper published in Diabetes Care in January 2008:
Effect of Cinnamon on Glucose Control and Lipid Parameters. "CONCLUSIONS— In this meta-analysis of five randomized placebo controlled trials, patients with type 1 or type 2 diabetes receiving cinnamon did not demonstrate statistically or clinically significant changes in A1C, FBG, or lipid parameters in comparison with subjects receiving placebo."