Tony,
I've been meaning to post about the "two weeks(') notice" thing myself. A few months ago I went on a kayaking trip with a few old friends, and the book "Eats, Shoots & Leaves" came up while sitting around the campfire one night (I'll cross-post this to thread1256-874493 since I'm walking the line between the threads).
We talked about the picture that appears on the back cover of the book. It is a picture of the author holding a large apostrophe on the end of a stick so as to turn the title of the movie "Two Weeks Notice" into "Two Weeks[red]'[/red] Notice." It was agreed upon by the group that the phrase "two weeks" is being used to describe the word Notice and therefore needs no apostrophe.
If it were just a bunch of boneheads, like myself, sitting there, I wouldn't bother mentioning this. But the group included an English teacher-turned-attorney and a guy about to complete his PhD in English (Composition & Rhetoric, precisely). These guys are good little scholars, and I'm sure that if they set about studying the subject, they'd find an explanation along the lines of what
sleipnir214 points to, but the point is that punctuation serves to clarify meaning. It is clear what "Two Weeks Notice" means with or without the apostrophe. In fact, I personally find the apostrophe jarring - it seems to indicate that the "notice" belongs to the "two weeks."
From what I've found online, there is a division among grammarians on this particular example. The apostrophe definitely seems more common, but an argument against it does exist.
[Slightly off subject]
For anyone interested, here is
an article from the New Yorker that has been quoted in many of the other articles pointed to about the book "Eats, Shoots & Leaves." It points out many grammatical and punctuation errors in the book. An example:
The first punctuation mistake in “Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation”…appears in the dedication, where a nonrestrictive clause is not preceded by a comma. It is a wild ride downhill from there.
It’s a bit long-winded (Did I mention it is from the New Yorker?) but worth a read.
[/Slightly off subject]
I now stand ready to be trounced for my comments.
-John