some people actually have wifi access everywhere they go (work, school, home), so the lack of a data plan is moot to them. however...i have had a data plan for years now, and cant imagine any of my phones without one!
I have wifi at home and at work, the places I spend the majority of my time. Catch is, at work, the wifi is subject to all the same firewall rules, filtering, and tracking that the wired network is. Not that I'm using my Droid to look at adult content or other non-work related material, but I like the freedom to do what I wish with it. For example, I cannot ftp to my personal web server from the Droid while connected to the corporate wifi. At home, meh, no big deal. Since I get good signal nearly everywhere with Verizon, depending on wifi is really a moot point for me.
You still have to be careful without a data plan though, I would think, without one, you're going to get charged by the MB.