Cash is good but I rarely carry cash, particularly popping down for breakfast
I've never had the charge problem although sometimes in this situation, I will be given a bill for $25.00 (particularly with the SPG breakfast benefit) and then told it will be taken off. I'll then add the tip, write a comment that it is a plat breakfast, and put a total of $5.00
While its annoying, I've never seen it show up on my room bill.