No it isn't. I tried to use my PowerPC Mini as a homeserver, but my gf complained about the constant noise, so I had to switch it off. The fan is spinning continuously.
G4 Powerbooks (PPC) were known to cause severe burns to people. So much so that Apple never called them laptops because you couldn't use them on your lap. (Granted, those people were wearing shorts and had the computer on bare skin, and the heat built up slowly so you didn't notice it).
Point being, the PPC Macs ran damn hot. My old G4 powerbook ran hotter than my current MacBook Pro. IIRC, notebook cooling and power requirements were the main reasons for the switch to Intel chips.
