You can delete pages in wiki by replacing all of the existing content with the word "delete". A page needs to be less than fifty characters long for this to work. (This page won't delete even though this paragraph says delete over and over.)
It is intentionally hard to delete pages. There is something poetic about making an empty page the delete request, but that is already detected as an operator error. Also the last set of edits made by a single person can be reversed through EditCopy. So the page doesn't actually go away until a second person deletes it too. Even after a page is deleted, an old copy can be retrieved from the HistoryPages.
An empty page is no longer (January 2006) detected as an operator error, apparently, since NewPage was recently saved empty.
Additional mechanics:
To begin with, knowing WhenToDeletePages isn't easy. When you're not sure, such as in ThreadMode, propose a deletion with a DeleteMe tag and let someone else finish it off, rather than unilaterally deleting it yourself. Before deleting, check all BackLinks and remove all references to the page you want to delete, but ReferDontDelete if there are too many links to fix.
Then replace the existing text with 'delete', but if the page has any content, however out of place on the Wiki, GiveReasonForDeletion, such as 'delete - OffTopic' or 'delete - moved to SuchAndSuch'. Don't use the word 'see' in this note, however, for that would exclude the page from the ShortWikiPages list. Also, when you want to delete a non-trivial page, it is good practice to leave the date of the last edit prior to the deletion. The next person can use this to decide whether he wants to confirm the deletion.
Before saving, making sure your UserName is set will ensure you aren't seen as an AnonymousDonor. It will mean the author has someone to talk to, rather than just recreating the page for an OffTopic dialogue. Of course it's up to you whether you want to be anonymous. Now save the page using a standard edit, so your deletion shows up on RecentChanges. Also, someone seconding can use the MinorEdit feature, so it is possible to see who both editors were. If the seconder does a regular edit, the first editor's identity is lost.
If you run across a deleted page you can:
Suppose I replaced this entire page with "delete". Then someone comes by and asks, "Why?". Too late. The EditCopy has been destroyed. Might as well just turf the page now. UseModWiki will fix this by using not a fixed number (in this case, one) of back up copies, but a time-expired set of back up copies. Cliff has come up with a brilliant solution to this problem. PageDeletion. -- SunirShah
Then again, in the garden of the perpetual WikiNow, the roots of a tree that was burned down in yesterday's fire may tomorrow provide sustenance to fresh seeds or shoots.
This issue was resolved by Ward with HistoryPages.