I had a bad flash once on a Gigabyte board. Not much happened really. As Ross points out. There is the backup to fall back on. If the board supports DualBIOS. The better boards offer this as a standard feature now. If in doubt, check if it has it.
While I noticed it did work as I hoped for. I did in the back of my head. Expect something to go wrong. There is a risk of it going bonkers while doing it. I always shudder that the power will go out half way through. Which is auto-bork for a machine. Since once you start. You cannot stop the update. Or your in for a world of hurt.
The reason I attempted a BIOS upgrade. Is that I read in the changelog. It supported a CPU I was looking to get, which the version I was using did not.. Otherwise I would of not flashed. Gigabyte BIOS normally, in most cases are hardware updates. Since on usual, the BIOS are pretty stable. I did eventually, get it to flash correctly.
Gigabyte does offer on the update pages, beta BIOS selections.. Just look at the changelog to see if it is worth the effort to try it out. In most cases. If your machine works. Wait for them to put it in mainline before updating.