First of all, yes, most HDMI cables are ridiculously overpriced. It's a scam.
However, this cheap ones do have their drawbacks.
I found them to be fine for a single direct connection with a display, but ran into problems when running them into a receiver (brand new Sony) then out again into the display.
The Xbox seemed to handle it OK, but the PS3 and the LG bluray player both got 'sparklies', pops and flashes both audibly and visually, indicating that data is being lost. If you look at the wikipedia page on HDMI, you can see that this is an established phenomenon with sub-par cables.
I just wish that there were cables that found a happy medium... around the $10 - $20 price point perhaps.