To get the officially compiled PoC5 client to mine on my Macbook Pro (Mavericks). I had to start it this way:
exec "/Applications/Ethereal.app/Contents/MacOS/Ethereal" -seed=false
Simply double-clicking the Ethereal.app downloadable and running it that way would not allow me to mine any ether. It also seems to get stuck on 1 peer and never connects to any other ones.