My opinion? There really should be no set rule for paddle length because there are many variables to consider. Do you kneel or sit? Do you heel the boat onto its side or do you stay centred? Do you "sit and switch" paddle or can you control the boat with correction stokes?
My own style of solo paddling (Canadian or Classic Solo...check out the fantastic Becky Mason DVD for more info) means that I'm always kneeling in the boat (never sitting) and I tend to heel the boat over and paddle on one side exclusively (tend to favour paddling left side). This means that the gunnel is near the water line and I don't have to reach over too far to place the blade in the water. More importantly, most of the correction strokes are based on underwater recoveries so the blade tends to stay submerged and shaft length can be shorter than average. Before I started making my own paddles, I found conventional paddle shafts were too long for my style of solo paddling.
I've personally found that 58 inch length works well as a guideline with blade length being anywhere from 28-32 inches long. Simple formula for me...58 inches is the length to my chin so this worked for me.