The way I see it, the driver is being paid by Mears to get me safely to my resort in a timely manner. That's his job.
To earn a tip, one is expected to go above and beyond. Tips have become far too "expected" these days. I have indeed handed a DME driver a couple bucks for providing a very professional (and understandable) spiel before the video, a fun "welcome to Disney" song when passing under the arch, and helpful and specific details regarding when to disembark (i.e. which resorts in which order, or which airport side to get off on).
However, if he/she just plops down, drives me to the hotel, and I get off with my own carry-on - that's not "above and beyond". He/She fulfilled their job duties.
And if a driver eats the microphone and rambles on unintelligibly for minutes about who-knows-what....that should be negative tip. Especially if he starts talking over the video, which is my "I'm here" tradition.
But that's just me.