robust email address validation through regex and javascript

Regular expressions are a representation of a grammar that helps computers and programs interpret and validate human input.  Unfortunately they are a huge time-suck and are a form of mental masturbation.  But one person's poison is another's Picasso; some regular expressions are like poetry to the mathmatically-bent computer scientists, and great debate has ensued over the best interpretation of RFC822, the internet's email address specification. 

Also, with the 16-Nov-2009 Internet Corporation for Assigned Names and Numbers (ICANN's) move to accept multi-byte, internationalized top-level domain names (IDN/TLD), I wonder how many hosts will need to update their assumptions in their regex.  Also I wonder what google mail, yahoo, amazon, ebay, facebook, or twitter might consider for their own RFC822 validation routines going forward.

Since there seems to be as many regular expressions developed and published as there are email addresses, I'll contribute what I've come across as well.  We'll see how this evolves in 2010 when people start employing these new domain names.

simple one in javascript (from Dustin Diaz):

var pattern = /^([a-zA-Z0-9_\.\-\+])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;

and a big one (from Paul Warren) - though I've yet to see an escape sequence for adapting this expression for use in javascript:

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