A couple of days ago OmniFocus was updated to its latest version, adding support for amongst some other things, Siri. Not having an iPhone 4S myself, I can't judge how well it works, but the idea appeals to me a lot.
Being able to through Siri create a new to-do item, on the go, without having to touch my phone really makes Siri become more of my personal assistant.
All Siri-created to-do items are saved to your inbox just like any quick entry items would have been. You can then choose to file them under projects and contexts just like you would any other item.
Additionally, OmniFocus has fixed a few bugs and changed the way items are sorted in Forecast mode, displaying inbox items at the top followed by other due items.