The backticks (\`) are a [Markdown][1] shortcut for what will later be rendered as `<code>` in HTML. Needless to say that this tag should be used to highlight actual code (or commands), not arbitrary words. 

To highlight keywords, the `<em>` tag should be used. This again will often be displayed as italics, so you get the same result by wrapping text with `<i>` tags.

From the Chicago Manual of Style (chapter 7.47):

> Use italics for emphasis only as an occasional adjunct to efficient sentence structure. Overused, italics quickly lose their force. Seldom should as much as a sentence be italicized for emphasis, and never a whole passage.

This is just general advice. Briefly looking over your posts, I don't even think that's relevant for you—but it might be for others. There's a certain trend where people use `code` for highlighting `everything` that could be remotely `important`.

See also: [Inline Code Spans should not be used for emphasis, right?](http://meta.stackoverflow.com/questions/135112/inline-code-spans-should-not-be-used-for-emphasis-right)

  [1]: http://daringfireball.net/projects/markdown/