BIOS flashing is only sometimes necessary and for the most part manufacturers say don't do them unless you HAVE to.
Most motherboards come with winbased flashing. It used to be somewhat iffy but I've had no trouble with either MSI's winflasher or ABit's Winflash utility. Generally the 'update from internet' option will sometimes give you a bad flash, but I've never had a problem doing the 'update from file' option.
The act of 'flashing' means you are erasing the previous information to install new information on your BIOS chip. If a flash goes bad then you've got a new paperweight
but i've also heard some people say something about taking out the BIOS chip and putting in a new one while the computer is still on, which confuses me to no end.
It's called hotflashing and is required to fix a corrupt BIOS chip. Read the article that MST3kGeek linked above for a better explination and procedure