Users with jailbroken iPhones who are also Twitter and Facebook users should check out a new app called qTweeter. It's a pervasive app that runs in the background, and lets you fire off a quick Twitter and/or Facebook status message without exiting whatever application you're using.
To use it, you simply drag down your finger from the top of the screen which pulls down an area for composition, along with a keyboard that slides up from the bottom. From there you type out your message, and if you've set up your Twitter and Facebook accounts you can quickly toggle which ones you want to send the message to.
You can also have it copy whatever text you've written, and paste it into another Twitter application you have on your phone, straight from its UI. This is nice if you're halfway through a message and realize you want to add a picture, or want to save it as a draft for later--both things that most Twitter apps can do.
What's really neat about this application, and where I think it holds a lot of promise over some legitimate iPhone applications, is that it can adjust its features based on what applications you're using.
So, say for instance you're listening to music in the iPod application. If you want to beam that information back out as a status update, you can do so with a special shortcut link within qTweeter that will insert that information into your outgoing message (along with a link to purchase it). It also does the same for Safari and YouTube, so if you're watching a funny video, or want to share the site you're visiting you can do it right there without leaving the application.
For application developers, having such an easy way for users to promote your app as part of a Twitter or Facebook status message would be nice. It's also a big convenience to have an activity that must usually be done in a separate application, in every application--just like Apple did by putting access to the iPod controls in every app.
QTweeter can be found in the Cydia installer application, and is free for the first 15 days, after which it will become donationware. You also (obviously) need to have your iPhone jailbroken to use it, which we're not going to tell you how to accomplish.