@Skud:
My Sapphire HD 5770 developed the D4000 LED issue, i.e. thermal diode going crazy even though there is no overheating happening. From what I could see on the internet, only Sapphire (the exact same one I had) and HIS models have this problem. There are a variety of fixes, from applying more thermal conducting paste to using a better aftermarket cooler, but in some cases the card was just plain bugged - mine was one such case. The display would go black after 15-30 minutes and the D4000 LED light would come on.
I gave it for RMA and have collected the repaired/replaced unit (I don't know whether Aditya infotech repairs or replaces). In the meantime, however, I got myself a 550 Ti and the system is running fine, so I'm in no mood to check the 5770 at this time. Will however keep the card for possible use in building a PC from spare parts I got.
But given the frequency of this issue, it seems that many Sapphire cards of that particular PCB revision has this problem. It was a non-reference PCB design, should have known better.
I used to think Sapphire was the gold standard for ATI graphics cards, but when a card develops an issue like that in 1.5 years, you don't get a good impression. My old GeCube HD 3870 (reference design) still works without any issues whatsoever and it's pushing 3.5 years now.......Same with some old Asus cards.
The last cards I remember developing issues within two years were XFX ones. Since this is a common issue with that particular model, I'd say Sapphire (and HIS, since it seems they also have the issue) cheaped out. Not to mention
Teapo capacitors on the PCB of the sapphire card, which are known to be lower grade components. Now even lower grade components will last long enough that you will never see a problem (electronic components are generally designed for heavy duty use), but it is an indication that the company cuts corners.
At the time I got the card, I didn't know better. Now that I had a good look, I'd say Sapphire should not be the no.1 brand to consider for ATI - they still make good cards but I think most people will be better off with an Asus or MSI.
Take my Palit GTX 550 Ti, for example: Compared to the Sapphire card, Palit skimps heavily on the bundle and cables. But the card has good OS-CON capacitors. It at least gives a good impression. What I can say is that Palit's fan blades are thin - if something gets stuck there or you pull the wrong way while cleaning, you could break them. Other than that the build quality is solid and I can say a bit better than the Sapphire. Let's see how long it lasts.
With graphics cards, you get what you pay for - the extra for the MSI, Gigabyte or Asus is well worth it in most cases (unless you know to take good care of your cards and really want to save some cash).
For what it's worth: I've not seen anything about this issue happening with 6770 models, and my issue may have been bad luck as I bought a specific model that had this bug, but the Teapo capacitors, PCB flexing, heatsink assembly (again this depends on model I guess), etc. - this is what made me think it wasn't the best in terms of quality. An Asus 5770 feels like a solid brick in your hand 
@Cilus:
GTX 550 Ti has 116W TDP. Converter cable wouldn't matter if you had 600W SMPS but most mid-range GPU buyers don't have high end SMPS units. Adding the converter cable is not optimal for electrical reasons: it adds resistive load and contributes to power loss. In borderline cases with a 450W or 500W SMPS, it is possible that not enough current can reach the graphics card, or it can be inconsistent, leading to instability and crashes.
One should *always* avoid the converter cables if possible, there's a good reason why the wires aren't all just connected one way and attached with converters to give you 4-pin, 6-pin, etc. (logically speaking, doing it this way would make the SMPS cheaper to produce) - the wire type is adapted to the kind of current passing through it. Changing it causes an effect which may be good or bad, but this effect is regardless one that you don't want.
). PM me if you are interested.
