To bridge the standard/metric barrier: 46C is 115F :: 140F is 60C :: 150F is 65.5C
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Under a heavy load, that's not uncommon for a G4 PowerBook. A lot of Seti@Home users have reported PBs reaching the 140F/60C level when running their program and other programs like it. On a side note, P4 based Dell laptops have been reported at over 167F/75C before......I've heard numbers for some of the early AMD64 based laptops...I'm still trying to figure out how they don't catch wood desks on fire.
You may want to reconsider your use of a laptop. Contrary to popular belief they are not truly a desktop replacement. Granted todays laptops can do the majority of things we need to do...that doesn't mean they're designed for it. The main goal of a laptop is portability, which comes at a cost. In order to be portable, you have to make some concessions. You also have a major heat issue when you run the machine flat out. Maybe a PowerMac would be a good idea to invest in.