BIOS

[CREDO]

As DS said, if your about to change hardware, upgrade the CPU etc then updating the bios is a good idea to ensure that your bios can support newer hardware that wasnt thought of when your bios was written. Or if you plan to put XP on an older machine then sometimes you have to update the bios in order for XP to install.

But for the average user as klepto said, if it aint broke dont fix it. Flashing the bios can lead to undesirable system performances if you screw it up. although all the new intel boards have a .exe to run that does it all for you, no need to manually flash it.
I would read through the changes the new bios has, see if any of the fixes are relavent to you and your setup.
Remeber to double check that the bios you have is for your paticular board, not just the chipset the board uses as flashing the wrong bios can permanently screw up your board and you might as well cut it up into nice little pieces stick it to a canvas and use it for a bit of techno art.