My thermometer is only approx. 2/3 full, which I thought was the main guide to whether or not you're overdoing things.  Portions of my level are admittedly complex, but I didn't think it was that bad.  Certainly, I don't feel my level is nearly as complex as the developer made levels.  The framerate is a bit choppy at times.  I'm going to go back and trim out any unnecessary and out of camera view scenery and maybe scale back a bit of motion.  Hopefully that will help a bit.  Anyone else battling this problem?  How are you addressing it?

Haven't had this problem. My thermometer is only just over half full though.

Like I said, I thought that this is what the thermometer was for, but now I really don't understand the role of the thermometer.

had this problem when I tried to use too many lights in one area only, other common problem is message that object is too complex and can't be changed/added to.

memory restrictions, frame rates, and resource management are someting developers have to work with constantly, just part of the process I guess.