I have settled on using curly braces when there is more than one line in the body
I'll throw another vote in this pile. I use no curly braces when the statement does not have its own block scope, and when it can fit cleanly on one line. If it requires two, I put braces on it. Since I put if statements on a separate line from what is executed conditionally, then that means that that is enclosed in braces, too. I do agree that extra braces reduces the possibility of human error; I may consider doing it all the time at a later point. In effect, I use no braces when the block looks concise enough that it can be readily understood as being the sole statement of the block, and that no more statements would be added. If I have to debug, I add braces, output the values, then remove braces when I remove the output code.
In my mind, where I parse the source linearly, a no-brace if statement gives me an explicit measure of what the conditional encompasses, and it looks aesthetically pleasing to my eye at how the simple things appear very obviously simple.
However, once I must team up with someone that is prone to human error in these kinds of places, I'd probably opt to ensure that we aren't each other's downfall.