Go to certmanager.net/sun and log in using the ID and password you entered when registering with SUN.
I checked that today. I had passed my SCJP on the 20th and from my account on that site, I found that they had mailed my certificate on the 24th. So hopefully I will get it within the week.
The entry was like this:
Mar 24, 2010 Mar 24, 2010 Fulfillment 5093105 Sun Certified Programmer for the Java Platform, Standard Edition 6: Mailed Details
Mar 24, 2010 Mar 24, 2010 Fulfillment 5093105 Sun Certified Programmer for the Java Platform, Standard Edition 6: Processed Details
Mar 21, 2010 Mar 21, 2010 Fulfillment 5093105 Sun Certified Programmer for the Java Platform, Standard Edition 6: Newly Created Detail
There, you can also check if you have entered the correct postal address. I had to make a few changes to mine.
Good luck