'm thinking of trying to find some black medical tape to wrap the corners in, but I think it'll get gooey over time. Did anyone do anything to cover the metal part's outsides up?
I've not had any issue like the Amazon reviewer described, and I often store my bodies with the RS-4 attached in a Lowepro Toploader Pro 65AW or 75AW.
However, I did previously cover the FastenR-2 D-rings - not for protection, but rather because when walking with a heavy-ish lens (70-200/2.8 IS II, 100-400) hanging on the strap, the metal-on-metal contact of the ConnectR-2 with the FastenR-2 made a clicking sound, presumably because of the shape of the D-ring on the FastenR-2 (it has a slight angle at the top of the ring, rather than being a complete semicircle). The click was annoying, and louder than my footsteps when walking on a trail - loud enough to startle birds/wildlife.
Initially, I tried what you mention, wrapping the D-ring in some black electrical tape - and yes, it got a bit gooey. So, I removed the tape and cleaned the metal, then coated the D-rings on my FastenR-2s by dipping them in Plasti Dip
(available in the paint section of Home Depot).
I specifically mention the FastenR-2, because once the FastenR-T1 (which mounts through a Manfrotto QR plate for easy switching between strap and tripod/monopod) came out, I replaced my four FastenR-2s with FastenR-T1s. The -T1 has a smaller, fatter, completely semicircular D-ring, and importantly it does not make noise when the camera moves. I suspect the FastenR-3 that is now shipping with BR straps and has a round hole would also be silent.
I wouldn't worry about that. I've used the Black Rapid on two different cameras now and so no signs of it's use at all.
I wish I could say the same. After over a year of frequent use, mostly with the RS-4 supporting a gripped 7D + 100-400mm, the edge of the nylon strap where the ConnectR-2 sits is showing signs of wear (fraying). So far, it's not frayed to the point where I'm worried about failure, but it will need replacement in the near future. Still, the performance of the strap is sufficiently good that another one would be a worthwhile investment (actually, I will probably just get two, since I've recently been considering a second one so I don't have to switch them from body to body, or maybe the DR-1 double strap to carry both cameras at once - something I haven't done to date).