Disagreement Brewing.. there might be something to that..
Don't put pots in the oven that have plastic handles.. goes without saying.
Simply boiling a full pot of water on the stove or burner is more than sufficient. The inside will turn black below the water level = oxide layer
Clean with tap water and a dishcloth only.. no need to do more.. no soap, no nothing.. rinse well after making sure the hardened scum is removed.
Finally, we've talked about everything but what you use to separate the hop sludge and grain bits from the wort. What do you use if anything? If you are using a strainer of some sort and it's not stainless, that may be your problem. Lick the strainer. Does it taste metallic ? If so, that may be your problem. Also, do you use something for containing your hops other than a cheesecloth bag? Consider everything that touches the wort.
As a last note. You may well be overanalyzing your beer and your reactions may be affected by your friends comments. How about taking a cold bottle or two to your LHBS and asking them to critique it for you. I'm fortunate enough to have a couple of judges at my shop as well as a number of friends who are most excellent brewers. They can always find something to comment on.
Don't volunteer ANY information when asking them to critique it as even seasoned brewers who find something wrong may/will attribute it to extract brewing.. and that, my friend is a lot of whooy. I've won a club competition with extract brews after watching others with their elaborate grain systems creating the same beer.