One issue I had with my EVO was not being able to easily tell whether my ringer was on or off. Sure there are icons in the status bar; normal has no icon, vibrate has a vibrating rectangle, and silent has a note with a slash through it. With everything else going on in the status bar, this just wasn't enough for me.
So I found myself doing Home>>Menu>>Settings>>Sound>>Sound Profile a lot. Sure you can use the volume rocker on the side or a long press on the power button to change it, but not in the middle of a call.
I searched some forums and looked at some apps in the marketplace and eventually found this widget from HTC that was already included on my phone.
Why HTC decided to call it Profile and not Sound or Sound Profile is confusing and made it difficult to find initially (and would have saved me a lot of searching).
With this widget on my home page I can clearly see if I am in normal, vibrate, or silent mode. Pressing it gives you a menu to quickly change the setting.