Do you need text/javascript specified in your <script> tags?

It's a Crockford recommendation. I know I've seen it echoed elsewhere (ppk maybe?). The HTML5 spec does not require it.

Oddly, it's become somewhat au courant to use the "type" attribute to mark <script> blocks that you don't want to be evaluated:

<script type='text/html-template'>
  <div> this is a template </div>
</script>

By giving a weird non-JavaScript type, you get a way to stuff raw text into the page for use by other JavaScript code (which is presumably in script block that can be evaluated).

See Crockford's write-up on the <script> tag, most notably:

Do not use the <!-- //--> hack with scripts. It was intended to prevent scripts from showing up as text on the first generation browsers Netscape 1 and Mosaic. It has not been necessary for many years. <!-- //--> is supposed to signal an HTML comment. Comments should be ignored, not compiled and executed. Also, HTML comments are not to include --, so a script that decrements has an HTML error.

...

type="text/javascript"

This attribute is optional. Since Netscape 2, the default programming language in all browsers has been JavaScript. In XHTML, this attribute is required and unnecessary. In HTML, it is better to leave it out. The browser knows what to do.