Any discussion of crank sets and 29"ers also has to include gearing options. It has been well documented that going to a 29 inch wheel increases your gain ratio by about ten percent. Not good if you have a lot of climbing to do. (And especially not good if you are not that great at climbing!)
So, the big thing with a lot of 29"er freaks is how to attain that lower set of gears. Usually the solution is looked for at the crank end, although alternatives exist in cassettes. In stepped Surly
with their Mr.Whirly crank set to fill that need. It is a highly configurable crank set that allows the use of small chain rings in the 20 tooth range. (See the Action Tec link above for some examples of these)
It should also be mentioned that Middleburn has made a crank set compatible with these lower gear options for quite some time. The thing is, these solutions are a bit overly complicated, high priced, and not always easy to get. Nor are they all that "new".
Once upon a time, the 94/58 BCD crank set was fairly commonplace. You could run your 20 tooth granny, you could bolt up a 29 or 30 tooth middle ring and you could do that and spend about half of what the current solutions cost you today. The one draw back? Square taper bottom bracket interface only. (And that is an arguable subject in itself)
My point today is that somebody needs to revive one of the old five arm, 94/58 BCD forgings in an ISIS compatible format and sell it for a reasonable price. My thought is that this crank set would sell like hotcakes, especially to 29"er freaks converting their gearing to more "mountain friendly" ranges. Will it happen? Well, let's just say that I am twisting an arm here and there to convince someone to do it. I'm not saying my influence will help, (Maybe it will hurt! Ha ha!) but I am convinced it should be done.
That about covers the crank issues I have unless we want to talk about "system integration" and "outboard bearing" cranks. Grrr! (maybe that'll give ya a clue what I think about those!)