First post, so forgive me if I violate any RV forum netiquette.
I work on the Internet for a living, so I have a lot of stuff pertaining to that and have done a ton of research on it. I currently run a pretty sophisticated setup, with two different wireless carrier cards (one AT&T unlimited Express Card, one Verizon USB) connected at various times to a laptop or two, phones, iPad, occasionally even a server, and a Cradlepoint router which I can use as a standard wireless router for about as many devices as I want to run (phones, iPad, laptops, even desktops). I also have a DroidX that I sometimes tether using PDAnet (paid version - its worth it).
I use A LOT of bandwidth when I can. Some months, with everything working, I find I can use upwards of 20GB/month, and I don't even belong to netflix
I really like having two providers, and that my ATT contract was written before limits. I'm hopeful I can keep it that way.
Anyhow - I personally use my phone on a tether as a backup modem, or for when I'm on the go and don't want to carry a card. When I'm running out of my 5GB/mo on my USB and need the connectivity that Verizon supplies in that spot, its a good option. I've found that using a backdoor app such as PDAnet works pretty well, and if I were just surfing or checking mail periodically, I'd think that it'd be enough all the time. I agree with the above thoughts on going ahead and spending the extra to unlock the secure sites - you have no idea how much is 'secure' until you can't get to it (Yahoo messenger, several news subscriptions, any banking/credit/etc. site). I've used upwards of 4GB/mo on my tether, but I try not to go crazy with it. I wouldn't download any large programs, or do netflix or play poker or such because I don't want to show up on the radar of the phone company and get limited. I usually run into town and find a wifi hotspot for that (Starbucks, McDonald's, etc. My favorite on my last stop was the supermarket - 3Gb/sec for free). I'd download the big files and then take them home.
As far as hotspoting the phone from Verizon - they want to charge too much and place too may limits for my taste, so I didn't even consider it. I like my Cradlepoint for that. As far as jailbreaking or cracking my phone, I'm not excited about that either, though I know a lot of people do it. Kudos to them, but I like my warranty, I like knowing what will work and how without having to tinker. Its an option for sure, just not one I use.
For me, the bottom line is: Tethering a phone using one of a variety of programs is very worthwhile, but don't try to push too many envelopes. There are plenty of articles about this via google, and all that I've read say pretty much the same thing - if you're doing it as a regular user without a heavy bandwidth need, or a RIGHT NOW speed attitude, it will work for you. If you're the other type of user, its probably worthwhile to find a different way.