I'd say never do it unless you really know that your card has a problem which can only be solved through flashing.
I had that issue with my 5970. It used to go grey-screen while in 2D mode when it under-clocked. Found on more than one source that bios flashing to a more recent bios which had been developed specifically to solve that problem would solve it (I had bought mine very early on release) so I flashed both gpu's bios and it worked fine since then.
In Feb 2010 I had a custom system made, which also included a sapphire 5970. From practically day one the card produced random artifacts in 2D. Complained the shop and they eventual sent it back, olny for the card to be returned, stating thre was no fault. Well that was cr#p, that day more random 2D artifacts.
I have not over clocked the card, its remained on factory settings. I only have started using the fans because it seems to get hot even in 2D mode. Between 55 - 59C is not uncommon. Then I hit it with the fans to cool it down. I also have a Antec 910 box and that has a heap of fan cooling so, it shouldn't be over heating. I clean the box and fans on a regular basis. I also have 1000w Corsair PSU, so it's not a PSU issue either.
I'm not a hardcore gamer, I merely like to playing games with all eye candy on. Since then I have all but gave up and have frustratingly put up with this issue. I still use the system and recent updated to Win7. However the problems have since got a lot worse since the updated OS. Albeit the card is no longer hot property but it still meets my needs. Plus I'm not cashed up enough to just dump the card and buy another.
Now not only do the 2D artifacts plague me but now the card is freezing too. When I pull up the cards Cpanel, the clock speeds are showing those which should only run in 3D mode. Most times it resets itself but others it give a BSOD. That's a total PITA when you lose stuff.
I'm not savvy with flashing bios, the last thing I flashed was in win 98 (well over 12+ years ago). Now with Win7 I'm totally clueless. So I'd like to get this issue fixed. Could someone give me some newbie tips and or point me to a link where it shows a step by step on how to flash this bios in Win7, thanks
I guess a safer option is, take it to the PC shop and get the tech to flash it.