Can the micro scratches lead to rust?
On stainless - nope. I do what Steve does.
EDIT - I've had the same 10 gallon SS pot for over 15 years and it hasn't rusted yet, so I'm assuming it won't at this point
. Now having said that, there are many different grades of SS allegedly, though I'm not aware of any that will readily rust. As someone who cooks alot, I can vouch for the fact that an iron skillet in a SS sink will leave rust stains on the sink. The sink hasn't rusted, the iron has leached out of the skillet onto the sink surface, and is easily scrubbed away. You need to be sure to passivate your stainless steel kettle periodically though, as mentioned.