When I hear "free soda" I hear "free diabetes and heart disease". Free soda is the worst kind of encouragement to have your employees living a healthy lifestyle. I'd love to hear about a company who seeks to provide fresh local fruits and vegetables at its snack table.
I really don't mean to come off as a Debbie Downer, but soda is such a terrible scourge on society as a whole.
The point is that these stupid small things make (or not make) you feel appreciated.
Although I don't hardly drink soda, having free soda available would allow me to believe that the company is willing to spend a few K/yr to say "We appreciate your hard work, have something small as a token of our appreciation"
Heck, I got at least one place to get caffeine free with sugar Coke, since I don't like the effects of the former and (at least back then) didn't have to worry at all about calories at that level. I was probably the only one who drank it, but it was a really minor effort for them to include it along with everyone else's preferences, and obviously that sends a message as well.
I'm with you about the sodas. They are free at my work (with a loose rule of one per employee per day) and I always say to my fellow colleagues that it's terrible, sugar sugar sugar.