Paul Brians, a professor of English, has compiled an extensive list of common errors in English usage. Although some may think he is too picky when he makes distinction between classic and classical or imply and infer, it's worth reading his explanations and even printing the list (if you want to print it, check this text file). There is also a book version of the site.
Some tech errors:
* A hard drive and a hard disk are much the same thing; but when it comes to removable computer media, the drive is the machinery that turns and reads the disk. Be sure not to ask for a drive when all you need is a disk.
* On the World Wide Web, a "home page" is normally the first page a person entering a site encounters, often functioning as a sort of table of contents for the other pages. People sometimes create special pages within their sites introducing a particular topic, and these are also informally called "home pages" (as in "The Emily Dickinson Home Page"); but it is a sure sign of a Web novice to refer to all Web pages as home pages. Spelling "homepage" as a single word is common on the Web, but distinctly more casual than "home page."
* In electronics, a jack is a female part into which one inserts a plug, the male part. People get confused because "Jack" is a male name. The cyberpunk term (from William Gibson's Neuromancer) "jack in" should logically be "plug in," but we're stuck with this form in the science fiction realm.