You have to have the $30 data plan(verizon at least) for the droid anyway. On top of that, if you want a broadband connection for a laptop, you'll need a $35 data plan with an aircard. So tethering is a huge deal. Little upset as I just got my droid a week or two before I heard of the Incredible
I think if you check the url below you'll understand what's happening. If you want to tether your Incredible it will cost you $25 per month (reduced from $30 "for a limited time.")
So for a device like the Incredible you're paying $30 for the "unlimited data plan" required for all smartphones plus $25 per month for "Mobile Broadband Connect" for up to 5 gigabytes per month tethered to some other device, e.g. a laptop/desktop/etc. In other words, $55-$60 per month.
If you have a netbook/laptop/aircard/etc that acts as a standalone device connected to the internet through the Verizon 3G network, it will cost you $60 ($59.95) per month. This plan also include VZW "hot spot" access, presumably to allow your connection to serve as a hub.
There is, however, both a confusing aspect to all of this and a "gotcha" that isn't clearly spelled out.
The confusing aspect is that Verizon also has a $10 per month (reduced for a limited time from $15) that appears to apply to "Android" devices and provides the same features as the $25/$30 per month plan. This appears to be a plan for non-smartphone Android and BlackBerry devices. As far as I know, however, there are no such animals.
The "gotcha" is that all of these plans put a 5 gigabyte limit on traffic. That is in stark contrast to the "unlimited" data plan you must purchase with any smartphone.
So what it amounts to is that if you DON'T tether your phone, your data access is unlimited. If you DO tether your phone, that access is limited to 5 gigs before additional charges apply. Just how Verizon plans to tell the difference between data being downloaded to a tethered device versus to a standalone device is a matter of conjecture.
Verizon Wireless - Mobile Broadband - Plans