About the only thing that can change the PQ of a signal that is within the digital domain is purposeful math; IOW, you need a binary mathematical operation to be performed, and a right-angle connector does not do that, so it can't change the PQ. A consumer digital video signal is really just a number (actually a very long series of 8 bit binary numbers) and the only way to degrade the PQ is to perform math that changes that number into a new number, a new number with rounding errors in it. As the numbers become less true of a representation of the analog original because of rounding errors, the PQ starts to manifest artifacts that degrade it. But again, a connector can't do that.
This is why the cheapest 3-ft cable performs just as well as the most expensive one; neither of them perform binary math, either by accident or on purpose.
But right-angle or funky adapters might increase the reflections inside a cable (probably do), and that can either be a problem or not be a problem. If the run is long, the aggregate reflection from all the connectors and cabling might go over a threshold where problems occur, especially if there are a lot of adapters in the signal chain. But as we have seen here already, multiple cascaded adapters, while they most likely increase reflections, are not likely to manifest any actual issues, at least in a short cable run situation.
As separate but parallel digital signals bleed into each other, or as digital signals lose their ability to remain perfectly timed bit to bit in series, which happens over long cable runs, eventually a point is reached where the signal becomes unreliable due to those timing errors (jitter) or multipath interferrence (the reflections interfere with the desired signal making decoding or D-to-A problematic). While that may intefere with the "quality" of the picture as perceived, it is not technically a degradation of the PQ as it exists in the signal. But that fine point hardly matters because perception is what is important.
A long HDMI cable at a small gauge can do this, and a poorly shielded HDMI switch box can also do this. The result is white sparklies in the picture, usually in a static pattern. This is normally due to the signal being reflected inside the cabling, which I guess could be the digital equivalent of "ghosting". Most short cables do not have this issue. But even though "I ain't afraid of no ghosts", this artifact is real, and can be a real problem in long cable runs.
What that means is that a better-constructed HDMI cable might avoid this issue more than a poorly-constructed one might, or a better shielded or better-buffered HDMI switch box might not suffer from this as much as a cheap one. So while you can get away with cheap cables if the run is short, it might pay to get the better cables if the runs are long, or to not buy the bottom-of-the-barrel HDMI switch box at Monoprice.
But that is certainly not an endorsement of Monster or Blue Jeans cables; while they may be more expensive I don't think that means they are really guaranteed to be any better. Odds are that they probably are (in that they may have better, less-reflective connectors rather than just better-looking connectors), but the premium might be too much to pay for, and you only need high quality for long runs.
Bottom line, insert the adapters and see what you get; if there is a problem it will manifest as sparklies, which will be the very threshold of the digital cliff. If you do not see those, you can be assured that the PQ has not been even slightly degraded.
Edited by TomCat - 2/19/13 at 4:47pm