I'm seriously considering leaving 3G data off when my phone regains the ability to use it. I've survived pretty well on WiFi only, and I have no reason to believe that will change when I get access to 3G data again. I am usually on WiFi either at home or at work, so it's only when I'm commuting or on weekends that the issue of mobile data actually comes up. When YouTube used up most of my monthly quota in a day, despite using the "preloading" function, I switched off 3G data. That was two weeks ago, and the only time it has actually come up since then was for GPS. Somehow, when I switched it on for 30 seconds, it claimed to use 2MB of data just to show me where I was. It's been off ever since and I've hardly missed it.
The things I do on my phone when I'm mobile are reading on Pocket (which is offline), making notes in Inkpad (which works offline and syncs when I tell it), banking and GPS. I do also listen to podcasts, take photos and check my action lists in Astrid. All of those are offline, too. I love portable computing, but feel like I can't rely on the network. If we're going to rely on services online we need either more reliable networks or offline capabilities generalised to any service. Thankfully, it looks like I might not have to rely on the mobile data network much at all.
Mokalus of Borg
PS - When I have 4G speed and a much bigger quota, it might be different.
PPS - But by then, my personal electronics might look very different.