W1zz has been testing PCIe power draw for a LONG time. I have personally been testing motherboards over the 8-pin connector only. Reviewers do look at these things with a critical eye that the normal users does not. So yeah, some people do.
AMD's 2900XT was popping motherboards at the 24-pin.
NVidia's GTX570 did as well.
If you pay attention, sure, there are a few cards that cause motherboard damage fairly consistently. For the most part, that's the whole reason why motherboard makers NOW include additional power for the PCIe slots, but not all boards do. There are MANY 3-x16 slot boards that support Crossfire that do not.
People that overclock should be aware of these sorts of issues in the first place, but the general "overclocker" isn't. There is much more that they aren't aware of. That's why I dropped OC, posting on HWBot, and put little focus on OC in my reviews. To me, OC is deep hardware analysis and testing, not a point-based skill competition like it has become. I don't call chasing numbers without a care at what dies OC'ing... and so I focused on GAMING as the main selling point. THe idea "Stuff dies when you OC" isn't true... stuff dies when you BLINDLY OC.
To me overclocking is an art. In order to make great art, you needs to understand the media you use, whether it be the paint, the pencil, music, or the hardware. However, mass marketing has hidden of all that as people have used OC as a selling feature.
Do a google on "burnt 24-pins". It's a hoot. Nearly every thread will blame the PSU. The real cause? Likely a VGA or a USB controller stuffed it. Not a single mention about that. Well, that's not entirely true. There are a couple, but still... when the blind lead the blind...