Resurrecting this old post, because it's cool and I missed it.
Proxi's dead (sob), but there's a newish web service that can do the same thing for you called ifttt (short for "if this then that"). (
http://ifttt.com/)
With this service you can set any number of triggering events, which can include an incredibly large number of online actions: emails, phone calls (a la the Jott suggestion here), tweets... all kinds of stuff. Once the event triggers, then it can do all kinds of things with them, again, linking together all kinds of online services.
To use this for ubiquitous task entry, build any number of "tasks" using the triggering events you want. In keeping with this thread, phone call and Twitter are key, although there are lots of services that can push out an RSS feed or send an email, so those are good options, too.
For the "do this" step, just have it send an email that triggers your send-to-Omnifocus email rule. Easy peasy, and no custom AppleScripting required.
Here's an ifttt recipe to work from:
http://ifttt.com/recipes/14744