Two issues
The 178 seconds to live article is an eye opener. My CFII spoke about that article a ton while we were motoring around for my 40 hours under the hood.
All good points in this thread. There are two issues at play for rated and non-rated instrument pilots venturing into IMC:
1)Hand/eye coordination and instrument interpretation skills.
The first can kill me if my skills are not up to snuff. I'll get behind, my scan can break down, I might miss something like engine gages, or miss a radio call. This is the first area where a VFR-only pilot can get into trouble. His/her scan is not tuned up, nor are the hands coordinated with what the eye is seeing. I remember my first attempts to fly under the hood: I was all over the sky, I was hyperventilating and overcontrolling. I did get it, eventually but the effort to keep it upright and navigate was very large. Once a pilot 'gets it', flying by the gages becomes as natural as flying is. This can (and does) get rusty, so profiency is key. Based on my performance during the first 5 hours of instrument instruction, makes me realize that if I had wandered into IMC before I had my instrument rating, I would have had a very difficult time keeping it upright AND navigating at the same time.
2)Spatial disorientation
This bad boy can trap any pilot any time, Inst rated or not. My Dad called it having "The Leans". I caught the leans three times. The first was during my first 100 hrs as a pilot. It was night, I was heading towards land over a dark ocean. It was CAVU. The lights on the shore were a brilliant line. All of a sudden, I blinked and they were travelling sideways. I did not have the feeling of leaning, the ship was straight and level, the shore was straight and level, but each time I blinked, the lights on the shore appeard to be travelling laterally to the side. My pulse raced, I sweated, but talked myself thru it. The second time I got the leans was during hood time with my inst instructor. I told him I had vertigo and he said, "Keep scanning, keep flying." It was hard, I complained, told him I felt sick, etc, but he never took the controls to allow me a reprieve, his theory was right on: Train the way you fly. I always fly alone, so fly myself out of it. The third time was in IMC, daytime. I was being vectored by approach control for the ILS. It was a bumpy ride due to mountainous terrain nearby, and for a split second during a long std rate turn to the left, I looked out the pilot's side window and spotted the ground thru a hole. When I looked forward into the milky white out the windshield, then back to the insts, it hit me Bam! The instruments said I was turning and getting tighter, by my mind said, "No way! You're level!. Keep it level or you'll die!" The nausea was overwhelming, I had an instant cold sweat and my heart rate went thru the roof. It took a herculean effort to believe the gages and roll level. I remember I shouted something out loud and forced myself to believe my attitude indicator. The Leans (or Vertigo) did not leave me instantly. Rather, it depleted slowly over time. By the time I was on the ILS, it was all gone. Until you've gone thru it, it's hard to describe. I've done tons of upset recovery and unusual attitude training, but I have never had vertigo in the process, in other words, the instruments always make sense to me, so I found it easy to right the ship. But with The Leans, the pilot must force himself to believe the gages or die.
I guess what I'm saying is there are two dark corners that will trick a VFR only pilot: knowing how to stay on the gages cold, and recognizing vertigo at it's onset and knowing how to escape it's grip (which, or course brings us back to Skill 1: knowing how to stay on the gages.)
So, heck yes, to be safe, train under the hood with a safety pilot. Not just for a few minutes 'till you're tired, but a 3 hour flight will all the radio calls, climbs and descents. And do it more than once. Or, you could do the same thing, the only exception is the safety pilot is a CFII and s/he signs your logbook, throw in some studying and a test. Bingo: you're IFR certified. Then you're legal to fly when all your mates are grounded by an overcast. You'll arrive to SnF or OSH days ahead of them.....
BTW, I forgot to mention: your insurance rates will go down.
Oh, and one more thing, achieving my instrument rating is way up there on the list of 'highs' in my life. But it isn't a one time deal: It gets repeated every flight I use it to get me from here to there. Staying safe and flying myself in weather to a destination give me a deep sense of satisfaction. Just like flying the perfect formation or the perfect loop or aileron roll.
Art