Ok so a few comments on what has been written so far,
First, from what I understand, cast iron is actually a terrible conductor of heat. That coupled with the fact that commercially sold cast iron cookware is generally very thick and heavy cause it to lose heat very slowly which is why it tends to sear better than most anything else. It's really all in the heft. HOWEVER, and I wish I could find the source for this but I believe it was in a random perusal of America's Test Kitchen, when cast iron skillets are employed on a stovetop, browning was found to be less even than other materials such as tri-ply or even non-stick. I imagine this will be disputed by some here, and again I can't cite the source but it would make sense given the fact that it's not a great conductor and stovetop burners are rather concentrated sources of heat. Consequently, it would follow that for a better, more even sear, you'd be wise to heat the CI pan in the oven on high for a good 30 min or so, then remove and sear on stovetop. Lastly, I believe the traditional way of cleaning CI skillets is to apply some course salt and run a bit of hot water and rub with paper towels.
For further reading on different materials' heat conductivity, check out this site
Common Materials of Cookware - Equipment & Gear - Cooking For Engineers