I might have borked the regexp a bit (I was writing it off-hand - and I see a stray [font=monospace]+[/font] in there now that I look at it and its handling of upper/lower case is off), but the idea I had when writing it was:
/events/archives/latest => /events/archives.php?date=latest
/events/archives/4-June-1684 => /events/archives.php?date=4-June-1684
So, "either the word 'latest'; or, one or two digits, a hyphen, then a word, a hyphen, then four digits" - the word supposedly being the name of a month.
The date format was of course just an example - I figured referring to the months by name was more human-friendly than "1684-06-04" would have been ("04-06-1684" wouldn't be a good idea). Needless to say, there's no way to prevent people entering dates that are out of range (1684) or outright bogus (Octember), but like I say, needless to say.... If they enter something that doesn't match the pattern, the rule won't be applied and the server would proceed as before. If they enter something that does match the pattern - you'll need to check user input anyway.
At the expense of a more complex rewrite rule, the day, month, and year components could be separated into distinct querystring fields, saving you a parsing step in the script.
Other ways to format the URL are of course possible. [font=monospace]archives/2011/06/04[/font], say. Then there'd be an obvious choice of URL for annual and monthly listings/summaries. (I seem to recall someone advocating the principle that if /foo/bar/baz is a legitimate path in a URL, then /foo/bar should be as well.)