QUOTE(numismatic nut @ Feb 3 2008, 06:53 PM)

1. Should I be concerned about my coin?
2. Did I put enough postage on?
I'll answer these together, because they are so closely linked to your answer

Yes, you should be
very concerned about your coin. You most certainly put enough postage on the envelope to send the coin out. However, from what I gather of your post, you sent the coin in a mylar flip, put it in a plain envelope with your submission form, and sent it off to the "grading" company.
First of all, you did not mention any form of tracking or delivery confirmation. Anything like this should go Registered Mail, so that it is for the most part "under lock & key", with its voyage being closely scrutinized. In the event you decide not to register the letter/package, at the very least you should always have Delivery Confirmation to confirm that "a package" was actually delivered to the company, as well as proper insurance in the instance that it may not have been delivered.
Even with Delivery Confirmation, you still do not have "proof" that the contents were delivered as mailed, nor that the individual actually received the package (even with a P.O. Box, it could have been "misplaced" in the wrong box, for instance). A signature is most definitely your best friend when delivering something to company you have never dealt with before.
Sadly, unless this IGS actually received your coin
AND they have some form of scruples, you'll never see your coin again.
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3. Why don't I have my coin?
It is quite possible they never received it. And even if they did, you have no proof that they received it. So, it is possible they are unscrupulous and will decide to keep the coin. Then again, giving the benefit of the doubt, they may have had a lot to do lately and it really is taking this long. If they are not sure about your attribution, they may very well have sent it to an attributer to validate the DDO. This will add more time to the whole process.
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4. What should I do next?
My biggest concern would be the simple fact of not responding to your inquiries. You should most definitely have somebody give them a direct phone call (their number appears on their website, from what I can determine), and make a direct vocal inquiry. If you do not receive an adequate response from the phone call, you most definitely want to put your request in writing. Write them an inquiry and send it via USPS Certified Mail. Someone will have to sign for it even through the P.O. Box. If they decide not to retrieve the letter and thus not sign for it, the Post Office will keep record of it. Certified Mail is the most widely accepted form of validating legal correspondence in most States' public law.
The payment form will also need to be validated. They accept check, money order, and credit cards. I am assuming that even with a credit card, the number was to be written on the submission form and they would then process it when they receive the submission form. This payment could validate whether or not they had received the submission form.
If it was paid via check, verify with the bank if the payment had been processed. If it has, then they most definitely received the submission form
AND the coin! Same with a money order. If it was a third party company's money order, it will take longer to validate, but needs to be done, nonetheless. Contact the money order company and request verification of the canceled money order. Beware! It could cost a few bucks to do so!
If it was paid with a US Postal Money Order, then you can have the Post Office verify whether or not the money order had been cashed/processed. You will need to have the original stub for the money order to do this. I would also suggest that you actually have the Post Master of your local Post Office verify the money order. Explain to him the situation and why you need to verify the payment. If the money order has in fact been processed, then ask the Post Master if he can initiate a Postal Inspector complaint for you to investigate possible mail fraud against IGS.
Finally, if the payment was made via a credit card, the credit card company will have to be called and an inquiry made with the payment amount and company name (International Grading Service or IGS) to see if the payment had been processed yet. If payment had been processed, then explain the situation to the card company and ask them if they are able to mediate with the merchant to open talks without a reversal of charges. If worse comes to worst, you can ask for the charges to be reversed, file a claim through your card company, and go on to the next step.
If no payments have been processed, then you may assume that they never received the coin. However, this may not necessarily be true. In fact, if they are unscrupulous and do decide to swipe your coin, it would be quite stupid of them to deposit or charge any payments!
Irregardless, seeing as they are located in Tennessee, after you have sent your certified letter, or if payment has in fact been processed, contact the Attorney Generals' offices of both your home State and the State of Tennessee. Fully explain the situation, what you have done so far to remedy the situation, and whether or not the company has open/kept communications with you and whether or not payment has been processed.
At that point, it's a matter of keeping your communications open with the Attorney Generals and IGS until the matter is fully resolved. Most definitely a long and slow process, but, in my opinion, the best way to take care of this matter. If either Attorney General decides that action is necessary to remedy the situation, also contact the Federal Trade Commission (FTC) and file a complaint, especially since damages had incurred.
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5. Did you use IGS before?
No, and like all other "graders", I probably never will.
Remember to always looks at
both extremes as well as the middle line. Consider all possibilities and act accordingly. Have patience. Always act in such a way that there is no cause for accusation against you, no matter how upset or frustrated you get over a matter. And let everything in life be a learning experience.

Best of luck to you and your coin!