I've had my layout set up for about three months. Everything is Aristo Craft brass except the four Aristo Craft Wide Radious Stainless Steel Switches. I used brass track clamps. So far there has been no problem at all.
I've been gradually switching my brass track to stainless. I have not noticed any problems, but I've put anti-corrosion paste on all the joints where I have different metals. I have some brass clamps, for example, on stainless track. I used anti-sieze compound from the auto parts store
On my track the trains tend to slow down a bit on the brass, unless it's just been cleaned. But otherwise no problem