Within the past three years I have purchased an HP laptop and eMachines desktop. Both involved numerous rebates. The checks kept arriving for at least a couple of months, but I think every rebate was honored.
I agree that it doesn't make sense for a visitor to the USA to expect to benefit from the mail-in rebates
You may, however, find that a big box store has an "instant rebate", a reduction in price taken at time of purchase. You could benefit from that.
Look in their fliers inserted in major Sunday newspapers. We have Best Buys, Circuit City, Office Depot and Staples (office supplies) near me. CompUSA has withdrawn from many major cities such as mine. MicroCenter and OfficeMax aren't in my immediate area though MicroCenter is about to occupy a store that CompUSA left..
seacue