rogue1979,
ERRR! There are at least 5 mainstream MB's that regularly read higher than 50C, under normal conditions: The Asus A7V, A7V133, A7M266, A7V266E, A7V266, and MSI K7T-turbo. They all regularly read in the 55-60C range. This is due to both thermistor placement and motherboard manufacturer compensation.
YOu can't make a broad based statement like "keep it under 50C". That isn't accurate, because each and every MB "reads" socket-a temps differently. There is no "general guideline" that can go beyond any single motherboard.
Yoshi64,
I did not list it as "accurate" like mbm because different versions do add "compensation" of some sort ot the CPU reading. Whereas MBM will read what the Asus ASIC chip is reading. However, this does not mean that the compensation is unjustified... it just happens that when people see "higher" temps they tend to freak, even though for certain mb's it is normal. IN fact, if they knew the Internal Core temps of a palomino from the SOLE palomino based review on the 'net (67C to 90C, they'd probably freak out more.
Mike