Sorry, been busy for a few days, looks like my post has garnered quite a few responses. I will try to address a few points:
(1) Tor is incredibly secure, and I would be willing to guarantee that those people who were busted were busted based on "good old fashioned police work," such as tracing the payment methods or infiltrating the group. If Tor is properly configured, not even your ISP (or phone provider, if you're on a mobile network) has any way of knowing what sites you visit. All they can see (if they try hard enough) is that you are connecting to the Tor network.
(2) If you have a properly configured rooted phone with the right custom ROM on it and have installed and configured some of the "power user" types of apps, you can effectively ensure that your cell phone provider (or Google) will not know what apps you have installed or what websites you are visiting using your data connection. And what they don't know can't be subpoenaed. This isn't an Android security thread, so I won't go into great detail, but suffice it to say that it can be done if you know what you're doing and try hard enough.
(3) I chose Hushmail because it allows you to create an account while you are connected through Tor. Most webmail providers filter for Tor exit nodes and refuse to allow you to create an account if you are using Tor, or give you "suspicious activity" warnings once you create the account and try to log in. Hushmail does not know who I am, so I don't care how trustworthy Hushmail is, since all they see is that someone originating from the Tor network logs into an "ourkansaw" account and gets a lot of emails from RIU forums alerts.
(4) The reason I am so digitally paranoid is because if I get busted for simple possession or something similar, I don't want the cops/prosecutors/etc. to be able to subpoena my ISP or mobile or Google records and discover that I'm regularly logging into a forum where I discuss growing pot, which might lead them to a much bigger crime and conviction. I also just generally try to hold true to the first rule for not getting busted: TELL NO ONE. If I'm not telling people who I know and trust, why should I turn around and tell my ISP, Google, or my mobile phone provider? That just seems dumb to me, so I take meticulous measures to avoid leaking this information to anyone who knows my true identity.
Obviously 99% of the time these measures are unnecessary, but the way I see it, if the tools are there and effective, why not use them?