I insulated my brewpot to get a better boil, but my 20' length of 3/8" copper immersion chiller was no longer good enough without going through an immense amount of water and time.
I took the existing coil, and attached two more coils of the same length in series for a total of 60' x 3/8" copper immersion coil.... it works really well.
It was not cheaper than a plate chiller, and actually more costly than a DIY CFC, but I decided on the immersion route because of: ease of sanitizaton, no possible clogs in chiller.
I chilled from 212F to 70F in short order (not sure exactly how long, but it was quick)
I got the 50' chiller from hopdawgs and hook it up to my garden hose and it cools the wort in no time. I attemped to make my own from 20' of tubing but I didn't like how flimsy it was gonna be.
yeah, Richard also bought a pre-built one. Its definately a good route to go.
On the flimsyness issue, one can make it rigid by using copper wire to make it more solid... something I should really do soon.