Wow, I'd say before you criticize people in this thread, you really need to understand how a PCV system works....and the intake system in general. Only one side of the engine? Cleaner valves on one side versus the other?
The PCV is just a pressure relief, the problem is that the air you are pulling from your crank case is full of vaporized oil and other hydrocarbons. When it's being introduced into your clean air intake stream, this exposes the valves on both sides of the engine to the oil vapours since it's a unified air intake stream...IE, one intake is feeding both sides of the engine, and you're introducing this dirty air flow to the main stream before it splits up.
From an engineering perspective, a catch can is good piece of mind because they are pulling oil that could have been introduced into the intake stream. This cannot be argued, and the visual evidence presented in these threads (and the threads across many other forums for many other manufacturers), demonstrate that the catch cans will collect significant amounts of oil that would have been otherwise introduced to the valves, cylinders and combustion cycle. Catch cans are not a snake oil product. They are a common feature on any air stream where you need the liquids/oils separated out in both automotive and industrial applications. Heck, every compressor I have at home and at my shop has a catch can to pull liquids out of the air. Keep in mind that many of our natural gas pipelines that are crossing the continent have filter/separators that are simply large catch cans on steroids.
Whether or not removing that oil will have a notifiable effect on the valve carbon build up is a source of many debates, but I'd rather be safe than sorry. As I don't have a direct injection engine, I can't show any evidence or experiences on my end that there is a impact on the valve buildup, but I am regularly emptying the crud out of my cans on a regular basis. I've also been running them on my vehicles for years now. I don't even run a fancy catch can, I constructed one myself using 1/2" fittings and an air compressor filter/separator, and it does a great job.