I tried the paper cup plan, but 1) it just feels so wasteful to be throwing away so many cups, and 2) I don't like they're a lot smaller, so I'd have to get more refills to equal what I'd get with the mug, and 3) I like being able to carry around remaining soda without needing to feel like I have to drink it all at once, and not worry about spilling it.
I mean, if they do get rid of mugs, I'll have to adapt. But it's not my first choice. My SF Membership already hinted that mugs will be coming for next year, so it doesn't sound like they're getting rid of them yet.