A countdown timer (currently hard-coded to 30 minutes) is installed at the bottom right corner. The screen can be blanked temporarily to black or white, useful when you want to steal the focus of the audience from the slides. Going full-screen (and back again) is also easy, this is important if you'd like to show some live demos during the talk. The slides look ugly due to the aging or faulty projector? Use the night-mode, something you have seen in the previous OpenStreetMap example.
When doing a talk about programming, it is often unavoidable to show code snippet. Thanks to Chili, the jQuery code highlighter plugin (there are other alternatives to pick: prettify, syntaxhighlighter, and many others), you will get the highlighting feature with zero effort. It's quite useful as the code fragment (which you likely show only for a few seconds) becomes more understandable. My favorite is however the live-editing feature, just press F3 to start editing the slide while you are showing it at the same time.
If you like this presentation tool, feel free to extend it. For example, you can have more presentation effects, like pulsating or shaking, by using script.aculo.us-based Presentacular. This example tool only supports basic editing, but I have shown a WYSIWYG HTML Editor before, so you can augment its editing features to support e.g. inserting images from the disk, changing character and paragraph styles, and so on. And of course, support for PDF export (with one slide per page) will be just very nice. A PowerPoint-killer, anyone?