Here’s another random UI tip for you, this one discovered by McCabe Maxsted:
Drag and drop an inventory item into the IM window to send it to the person you’re IMing with. You don’t need to open their profile window! (This doesn’t work for group IMs, though.)
The next version of Imprudence will have a little reminder note in the IM window, but you can do this with any SL viewer right now!
The more you know!
You find out the darnedest things, looking through the viewer source code.
For example, if you Ctrl-click on a slider bar in the SL viewer (or Imprudence), it will reset that slider to its default value.
The more you know!
P.S. This is what a slider bar looks like: 
I’ve written an LSL script which “serves” custom-generated HTML via a neat trick I discovered. But don’t bust out the champagne just yet — this method is extremely limited, so I don’t expect this to revolutionize HUDs or anything like that. Still, it’s a fun curiosity.
The trick is this: If you use text of the form “data:text/html,[html code here]” as the web URL, Firefox (and maybe other browsers?) will render the HTML code as a web page. For example, visit data:text/html,<html><body><h1>Oh hai!</h1></body></html>