This is the way I do it,
when I buy something that I think the price will go down within the next 60 days, I put a reminder on my ipaq to check the price 50 to 55 days after I buy it.
Then if I find it for a lower price ($10 or more lower), I call up amex, file a claim, take them to the web site (it's usually a online place that has it cheaper), fax in my original receipt, wait 2 weeks for a check.
If there's something I really want, then I buy it from a local store (BB, CC etc) and do the same thing, wait 50 to 55 days, then call amex and get a check for the difference.
I've asked my gf to get a blue card so I can double the limit to $2000 PM per year

($1k per card).
Last year, I was able to get a little over $600 in refunds from amex within a 80 day period.
not to mention the $1k in rebates over the last calender year
To save yourself the trouble of filing multiple claims with amex on the same item, just wait till you're close to the end of the 60 day period before you file the claim. Unless ofcourse you see a killer deal in the mean time on the same item, then go for it!
Good luck! My scanner should be delivered tomorrow which means I will be calling Amex on either March 21st or March 26th
