So far, everybody I've spoken to at CompUSA (local and 1-800-COMPUSA) told me that we could get 2 rebates, but the 2 people I contacted at PNY said the limit was 1 per customer. But today, at 12:44PM Mountain Time, Sammy at PNY said the limit was 2 despite what was written on the rebate form, and this was a change in policy from a day or 2 ago because they knew about the CompUSA newspaper ad.
Update: Being the obsessive compulsive that I am (and having been burnt by weasels at other companies who gave me wrong information and then lied about it), I phoned PNY again, and at 2:23 PM Trisha said that each customer was eligible for 2 rebates. I didn't even ask her this; I simply mentioned that my call was about the CompUSA memory rebate.