Before we can talk about Keywords in Anchor Text we need to define what in the heck this Anchor Text is.
Anchor text is also known as: link text, link title, or that stuff in between the <a href=""> thing and the </a> thing.
Here is an example: <a href="http://www.galaxywebsitedesign.com/">Galaxy Website Design</a>
The http://www.galaxywebsitedesign.com is the link url. The Galaxy Website Design is the link text (or anchor text).
When another website creates a link that points to your website that is a good thing.
Google, and other search engines, consider the fact that someone bothers to create a link to your website as a vote of confidence. So if want to bad-mouth a website do not include a link. Google will interpret the link as a vote of confidence in the linked to website.
So what about the "Keywords in Anchor Text" thing?
Quite simply, if someone links to you with the following:
<a href="http://www.yoyodyneindustries.com">Crystal Quantum Meditation Devices</a>
then Google will assume from this link that you consider yoyodyneindustries.com to be related to meditation devices. So not only will you increase the page rank of the yoyodyneindustries.com website in general. You will also add credibility to the keywords meditation and devices (as well as crystal and quantum).
Thus not only are links to your site important. It is also important what text is used in the link text (anchor text). If possible, find ways to encourage the use of keywords in anchor text used to link to your website.