So....here is my theory on blueberries in the smoothie (I had one that just about turned my face inside out!
).....The ration of fruit to skin is not ideal for something like a smoothie. Fruit skin is bitter in order to discourage getting fed upon....the good stuff is obviously on the inside. Its not to bad when you're eating blueberries one at a time or whatever....but when added to a bevy of vegetables, some bitter in their own right, it throws things off. I tried adding more blueberries (just made the problem worse) and honey (worked well, but I wasn't cool with added sugar). Stevia, like you said works best in the end.
I've been good....I spent my weekend half outside, and the other half in front of the computer trying to decide which direction I'm going to head in as far as my grow, nutrients, soil, etc. I think I read the entire internet!