Diamonds is bullshit, 0.5 extra discount per domain on top of golddeal.
The suggestion about hit them up is also a rumor or idunno... I contacted them in Nov/Dec 2011 about transferring them ~250 domains if they can give something better than 'diamonds' but they refused to do so, so i am keeping those at godaddy where i was able to renew them for cheap.
I like namecheap, they are just not that cheap anymore.. :P
They have occasional coupons tough:
http://www.retailmenot.com/view/namecheap.com
http://www.fatwallet.com/search/inde...uery=namecheap