Guess I'll be the salmon today.....
Yes plaid is effective and has been used for many years. Countless game animals have been killed using it. Countless others have not been killed while using it. You can and will kill critter while wearing it. However, is there more effective camo out there? IMHO - absolutely.
Personally it is my experience that Leafy camo and ghillie suits are far better then plaid at concealing movement and breaking up the human form. I also believe that open patterns like ASAT and predator have been better for me at breaking up the human form in certain circumstances.
All depends on what you want. I once killed a deer at 15 yards wearing a white tee shirt - still I personally believe camo would be a better option then a white tee shirt.
Deer do see movement more so then stationary targets. Where effective camo comes into play is when you must make some movement and still remain undetected. Yes by all means wait for the right time - however, I don't think I am the only one that has had to draw while I had a group of deer present. My ghillie and bow blind made it possible. Had I been wearing plaid I am sure most of the time they would have picked up that movement. Sitting in a tree after leaf fall most plaids do little to break up the human shape at any distance and tend to blob up like most camo does. This is where camo patterns like horizon, fall gray and ASAT work extremely well. Shall we talk snow?????
Bottom line for me is that wool plaid works great.... but the right camo, in the right circumstances/environment just does a better job and increases the odds that you will remain undetected.
Having said all that, there are those days where the tradition of wool plaid just feels right..... and I still wear it frequently.