I have never seen a single line reefing system which actually worked very well. There tends to be a lot of friction, much higher line loads, and an absurd amount of line to haul. I have actually removed single line reefing from a couple of my boats after not being able to get decent sail shape when reefed and not being able to get a reef in quickly enough.
Jeff, I use single line reefing since almost it appeared as an option on new boats more than 12 years ago. They evolved a lot in what regards the force needed and efficiency but I agree that two lines, or the old system whih only a line work better.
One of the biggest advantages of modern rigs is the ability to reef without going out of the cockpit and that translates in a much safer sailing specially in small boats (less than 50ft) and difficult weather. You can do it from the cockpit with two lines for each reef but that would translate in 6 blocks on the mast and 6 blockers on the cockpit and a huge number of lines. That is not practical.
Regarding sail shape, after many years of use I think the trick is to control the reefing lines with the high of the boom (trough a top lifting), I mean having the boom high when you reef and then putting him on the normal position given shape to the sail.
Also in what regards friction there has been a big evolution and on my actual boat you can reef by hand only using the winch to the last adjustment and not always needed.
Of course, if you sail with a crew you can always use the old system and go forward to pull down the sail till the reefing point and hook it while someone is letting it down and then have a single line to adjust the back of the sail, but for that you need a crew and have to leave the cockpit.