Date stamps make sense when you're talking about something specific to a point in time. The newest release of MozillaBrowser, for example. You'll find that most things discussed on Wiki aren't like that, however, so it's probably best to avoid datestamps generally.

A good rule of thumb might be to imagine strangers reading your words in a year. Will they care about the date? If so (for example, a WikiGnome running down backlinks to AreYouThere or DeletedUnlessDefended), put it in. If not, leave it out. Better still, write in a way that doesn't require datestamps.
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'''T''''''hisIsWikiAfterAll'''

If on the other hand you use Datestamps to identify the page version in a stored filesystem or database, DatestampsAreUseful. Also as recorded on the bottom of this page, a Datestamp is used to indicate the last edit, certainly '''not''' harmful. ItDepends on the User and Use as to whether Datestamps are useful. If harmful to you as a user, don't, if useful to you as a user, do. If you don't like a Datestamp on a page, Delete it. T''''''hisIsWikiAfterAll. If someone deletes a date you want to remain, restore it. T''''''hisIsWikiAfterAll. 

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See WikiNow