The following is an email reply I recently received from CommonSenseRC

"Our Ultra-Balancer does in fact operate below 3.7v per cell. At the the top of the unit, are three lights, which indicate average cell voltage. Red = 4.15v - 3.7v
Green = 3.7v - 3.2v
Yellow = 3.2v and below
Ultra balancer instructions: http://www.commonsenserc.com/product...ions_final.pdf
As for your question on how much imbalance is tolerable, you don't want to have any imbalance at all on your pack at all. What we define as imbalance is a difference of 50 millivolts between cells, or 0.05v. Anything greater than that needs to be balanced right away."

I've noticed that an imbalance of even 0.03v between cells after being fully charged results in slightly more fallback immediately after charging (0.24v) to say 12.20v instead of 12.43v. Whereas, if all three cells are within 0.01v of each other (4.14v / 4.15v / 4.14v) the Lipo will only fall back to 12.43v from 12.45v. (It is recommended that LiPos be charged to 12.45v not 12.6v)

Is some of this knit-picking? Maybe, but it does make one aware of the need to treat your LiPos with care to get the most performance cycles possible. Some mistreat/abuse their LiPos and then blame the vendor for selling them a crappy battery.

Hopefully, all this is starting to make some sense as you get a better picture of what seems reasonable to your own needs and budget.