Never say “New”
I just came across a site where the front page features the word "New" fairly prominently in a couple of places, including the description of the site. The site was last updated in 1999. Another page on that site refers to statistics "for April" but doesn't mention which April.
My advice (which I have often failed to follow, but have generally regretted failing to follow) is to always put a date on every page (including year), and never use the word "New" on the Web. Everything is new when it first goes up; the problem is that, if you're like 90% of the site maintainers out there, you'll add new "New" stuff without removing the old "New" labels, so that items that are new today will still say "New" two years later.
When I kept a paper calendar-book (and, later, a DayRunner kind of thing), I kept a lot of birthdays in it, and every year I'd have to painstakingly go through and copy all the birthdays from the old one to the new one. The trickiest part was that I listed how old each person was on that birthday, and so I had to increment that number for each person each year, and sometimes I'd lose track. Eventually I figured out that if I just listed their birth year, I wouldn't have to change the listing each year.
Similarly, if you put an explicit date on a document, you'll never have to wonder, three years later, what exactly you meant when you wrote "New" at the top of it. Nor will your readers.