Let's bring this back one more time...
I made one today. 50' of 3/8" OD tubing. Based on some of the talk about kinking tubing, refrigeration vs soft tubing, etc, I was hesitant at first. But it was easy!
Go slow and be gentle. I used a piece of string to measure 25' (the center) without unwinding the coil. I then coiled around a paint can once on each side of the center mark.
You will need to carefully manipulate the coils to wrap the tubing tight against the paint can; partial unwinding/increasing the coil diameters will be necessary. By the way, a paint can is 6.5" diameter, in case you're looking for something of similar diameter.
Step on the coil of Cu tubing at the mark, and pull the tube tight to the can. Also push the coils together/down so they are uniform. I thin I made 12 coils on each side of center.
Leave about 2' uncoiled at the ends for the flexible tubing.
When it's time to expand the coils to join them together, I rested them against each other by laying one coil on its side, which puts the other on top of it... and very gently the coils apart one at a time so that I didn't over spread them -- I wanted to keep the "cage" tight. Once the coils are meshed, push the outer edges in to push the coils into a manageable width (measure your kettle before you start).
Here's a picture of the tubing I used from Lowes. It was $47, the vinyl tubing was $7.50, and the adapters to get from faucet to garden hose to tubing barb were ~$9. So I'm in for ~$60, which is much cheaper than a 50' IC from a retail outfit.
I am currently brewing 2 gal batches in a 3 gal pot. The IC is a bit tall (and bulky), but I plan to upgrade to a 10 gal kettle for 5-7 gal batches soon.
I used it for the first batch today; an Imperial IPA. Using fairly cool tap water (this is Illinois), I was able to get from 212F to 135F for my hop stand in 1 minute, 22 sec. I thought that was pretty impressive. I didn't time the 135F to pitch, but it did take much longer. I can only imagine how fast it will be in the winter...
Thanks for all of the great ideas!