Currently, many companies are using Twitter for their service updates or company announcements (or, in the case of the news, for headlines)...but they aren't allowing the users to interact with their sites/apps in the other direction.
Akin to YubNub, I think it's high time that web apps start looking at Twitter as their Command Line Interface. A way for me to quickly retrieve data, like addresses from local search (as in the example I concocted above for a Yahoo!Local search), to send in information (i.e. sending your timetracking to Harvest, or a command to Blinksale to invoice a client, etc.).
We have many options we for Onramps, but I think Twitter provides a really useful, simple baseline to work with. Perhaps it will be their ultimate business model?
Hell, if the web apps don't build it, we could always do some experimentation with this over the next two days of the Mashroom. :)