The phrase "click here" is often used as hyperlink text in webpages, like so:
For more information on Veeblefetzers, click here.
This is frowned upon as a usability / accessibility faux pas because it separates the link from its context. Links stand out in webpages and users quickly learn to locate them visually. If Melvin comes to your site looking for some Veeblefetzer info, you want to make sure he finds it without too much trouble. If he scans the page's links first, "click here" isn't going to tell him anything; he'll need to hunt around the link to find out its relevance.
An irritation, you might agree, but hardly a great inconvenience. But now consider blind visitors; they may rely on a number of assistive technologies to help them browse the web. A common task is to build a list of all links on the page, so that they can be referred to quickly. This is starting to appear as a feature in browsers - Safari has it, for example, in the form of a bookmarklet. A "click here" link in such a list loses its context completely; there's no surrounding text to hint at its purpose and it might as well read "unkown link".
Similarly, it can be a time-saver for blind users who depend on a screen reader to skip through the links of a document with the tab key. Here we have the same problem - when a "click here" link is tabbed to, there's no clue (other than the target URL, which can often be lengthy and cryptic), as to where it will lead.
Since "click here" links carry no useful information and depend on their surrounding sentence for context, they are superfluous. You can rid yourself of them and increase your page's usability by selecting the text of your links to highlight their function. For example:
We also provide information on Veeblefetzers for the curious.
The phrase "information on Veeblefetzers" tells the user all they need to know and can safely be lifted out of its surrounding context.
In short, your hyperlinks should be able to stand independently, as they may be required to do so.