I don't know about more recent processors, but I have my C2D E8400's base clock up to 390Mhz instead of 333Mhz. The thing I noticed though is that increasing the base clock (with my setup) also increased the DRAM frequency and the PCI/PCI-e frequency. Also, some devices may not be able to handle the higher base clock.
As far as it being bad for the CPU, my overclock is completely stable and has been for about a year. However, I wouldn't mind getting some insight to this as well.