5GB, well it depends. My record for a month is about 38GB, but I tether almost constantly. I'm pretty sure most people on droidforums.net tether, which is why maintaining an unlimited data option for LTE is VERY important.
Anyway, when I hada feature phone (enV Touch), I used like 100mb, that was just browsing the web occasionally. I got the Droid X/Incredible, started tethering, and monthly data usage shot up to about 20GB/month on average. So it depends on how often you will use your phone's data.
As for what I think will be Verizon's plan for LTE pricing for smartphones, everything will remain the same. Unlimited data may go up to $39.99/month, but I doubt it. What's the point of 4G LTE if it's capped? Verizon advertises Skype video chat on its 4G smartphones, there's no way you can video chat a decent amount as well as do what you already do on a smartphone without going over a 5GB cap. Even a 10GB cap would be pretty easy to hit, without tethering. Besides, what about the people who live in rural America? Charge them for 4G they can't even get yet? Yeah, right. Actually, I think Verizon will let you pay for unlimited 3G, then you get limited 4G allowance every month. It's not what I want them to do, but I think that's what they'll do....
The reason I am so concerned about 4G smartphone pricing is that I have to know whether or not to sell my Droid Incredible , if 4G is capped, or unlimited is more expensive, I have to stick with 3G and my Incredible...