On my Macbook Pro, the "average battery impact" (last 8 hours) as reported by Activity Monitor is 1.2 (not sure what's the unit, but it's a low value compared to other apps), and we use it daily for work so it's kind of active the whole day. I wouldn't call it a CPU hog by far.
2) The CPU hog thing is very inconsistent - it probably doesn't affect all OS version/hardware combinations or they would have solved it since long ago. All I know is that I regularly see the client go to 80-100% usage of one core for a rather long time, meanwhile taking forever to sync just a few files - which clearly shouldn't happen in an application that mostly does IO. There are probably certain file types it has some problems with, but I didn't have the patience to analyze it yet, I simply switched to SpiderOak.
So no, I just can't trust their code quality.
* I've had two instances of near data loss where I could only recover data from the local hidden cache folder that gets deleted after a week. It had to do with a user error with moving out files from the Dropbox directory when the client was off - previous versions in the webapp can easily become corrupted this way.
* the Mac client is a total CPU hog since Mountain Lion.