Paddle length has always been a big issue for me...I'm no expert but this is what I think.
I've been sup'ing for a couple of years now and made myself quite a few paddles and found a length that I think is just right for me.
I'm 6'4" (sorry I don't have all my metric/inch figures in front of me right now) but I use a paddle that is 13" longer than my height..and think it's perfect..Here's a pic..

Not long ago I started looking at different paddle sites thinking about buying myself a nice new carbon job..and to my surprise I found that some sites said my paddle should be 6" above my head height...Jeeez..I'd be paddling like the hunchback of Notre Dame with a paddle that short.
I found a few sites that said 8" above head height...and only one that said 10" above head height....I was starting to think I'm a freak or something.
Yesterday I received my new 'How to stand up paddle' DVD..
..it's great btw...Anyway..I was rapt that in the dvd they say that the paddle should be between 10" and 12" above head height...Considering I'm a giant 6'4" that seems about right.
I think rather than inches above head height it should be a percentage of your height..A hobbit may get away with a paddle only 6" above his head height.
I feel sorry for those who have cut down their nice new $500 carbon paddles way too short.
I should also say that although I paddle almost every day..but I paddle mostly flat water and paddling in the surf may require a slightly shorter paddle..but only slightly shorter...I also should say that maybe my arms have stretched from 30yrs of windsurfing..but my knuckles don't drag on the ground when I walk..

Anyway that's my 2 cents worth..It will be interesting to hear what others say about this....also all you guys coming to the Mambo at Merimbula this year..
http://www.acr.net.au/~msc/default.htm ..bring your sup's.
David John