I guess I'm just going to beat a dead horse here, but I can at least be part of the statistics...
I saw this thread on the 16th when it was 2 pages, so I downgraded to 3209 as suggested. Not that I had any issues with battery life, but I figure, might as well.
I have been keeping an eye out for how fast/slow the battery drops... It either feels exactly the same or... it drops faster! But I'll just settle for stays the same. Definitely didn't feel like it improved any battery life.
I considered upgrading MS to get rid of the pesky red badge reminder on Cydia, so I returned here to see if anyone has any real concrete, positive improvement on battery life. I had come to the above conclusion BEFORE i returned to this thread. BEFORE I read Saurik's response, so my perception wasn't biased from what I read.
So now I'm back to the latest mobilesubstrate.
On a related note: I was also running winterboard before, but had stopped using it because theming icons for PvZ would cause it to crash, so I decided to just not run any themes using winterboard at all. To be honest, I didn't feel that the battery life had improved at all... It felt the same as when I was running LockInfo + HTC plugin + Classica 3 icon set + Nexus One live lock wallpaper AND Nexus One live home wallpaper.
So group me as one of the folks who believe that winterboard and mobilesubstrate are not the battery drain culprit.