Looking at a colleague's website (organicJar.com) and was jealous over the Feedback button on the side of the page of that website. It's an AJAX'y button at the side, themed so it stands out well over any background content, and plops up a nice form letting visitors give feedback. See the image to the right. It's of course important to get feedback from your visitors, to engage visitors, and perhaps if they have a good experience on your site they'll return again in the future.
On a stock Drupal site there are two ways to get feedback and engage your visitors. One is the Contact form, enable the Contact module and set the permissions so anonymous visitors can send you messages. The second is the ability to make comments. Enable the Comments module and set permissions so anonymous visitors can leave comments, it's also recommended to enable the Captcha module to reduce SPAM comments. Both of those are available on Wordpress (used by organicJar) so it's leaving me wondering why organicJar also has this Feedback button. One reason is the Feedback button appears to be pretty darn friendly, and it contributes to an overall friendliness factor.
The feedback button used on organicJar comes from Skribit. It's a whole service in which your visitors can vote on topics and see the feedback left by others. The sales pitch is to "cure writers block" by helping your visitors tell you what's most important to them. They don't have an out-of-the-box way to install it on a Drupal site. But there are two Drupal modules which do similar functions.
Feedback 2.0 does the style of feedback thingymajob where there's a simple text thing floating at the right. The user clicks on the widget, a form pops up, and they enter whatever they want to say. It works pretty well but for a couple flaws to be noted further on.
Any message given by your users is entered into an administrator-only reports section. It links to the node to which the feedback refers. It does not send any email notification though perhaps a trigger is available to do so. It may be important that feedback be public, and in this module feedback is private to the administrators. It's also not configured so the feedback becomes an opportunity for dialog with the person who left the feedback.
Another flaw is that the text of the feedback button is not visually set out from the background. Instead it visually mixes with the background and obscures whatever is in the background. Sometimes the obscuring is pretty severe.
Feedback & Suggestion Tab is a newer module that's visually more like the Skribit widget. I'm certain that everything Skribit does can be implemented as a Drupal module so why should there be a dependency on an external service? However this module is currently market Beta and basically does not function.