Croissant
When i took up pastry classes, making croissant is a dream, and I learned the technique and recipe only to be disappointed that in my city where temperatures are always high, my Chef instructor told we can only bake croissant using crisco shortening. Yikes, I cannot do that knowing the health hazard of hydrogenated fats. So, gave up and beyond the required class assignment never thought of baking. So we reading the BBA by Reinhart, and the so called winters here the temperature dropped to 20 Celcius, and Kitchen is cooler, so I followed that awesome recipe and and since past one week baked like 8 dozen of these flaky, light buttery delights called Croissant.Of course that was for friends and family and some I sold. 
I leave the dough in the fridge for 2 days and then fold and then again leave the folded dough for several hours in fridge and that gives such an awesome taste.
Here goes some images:
I am not sure that the hydrogenated fats in a small amount are all that hazardous. I make my pie crusts using them. However, I am with you on using butter for croissants!
Ford
We use to use butter for pie crust but we switched to lard a few years ago and I think the results are noticeably better. It is funny how fats come in and out of fashion, animal fats where demonized starting in the '60s but seem to be considered less fatal today and now the animal fat replacement the trans fats are the killers. Moderation seems to the answer to most of these things.
Gerhard
I too have used lard for biscuits and for pie crust. It can't be beat for flakyness.
Ford
Still working on shaping them neatly.
I'm curious why your instructor would tell you to use Crisco and not butter? A matter of fact if you want the best results you should use a European butter which has a higher percentage of fat in it. What type of butter did you end up using for your latest bake?
Yours look like they must taste great in any case.
When you dare, you should check out Txfarmer's post on TFL about SD croissants. Her's are as close to perfection as you will ever see.
Hi, Crisco or Unipuff remains solid at room temperature and easier to handle for laminated dough, we live in a city where average temperature year round is above 23-24 Celcius and bakeries and not airconditioned so are the home kitchens. Butter tend to become soft very fast and would complete melt and be messy beside being extremely expensive. However, I use butter for all my bakes, we get a non branded dairy butter that is non processed and unsalted that comes directly from farms and they are totally super in the croissant, you can actually taste the real butter then just any greasy fat. I am a weekend baker, meaning take orders to bake once a week for a small group of people. My croissant got hit with them, just because it taste different because of pure butter, then their commercial bakery and store bought counterparts. I am still working on shaping them neatly.