I just bought the Hitachi 4GB Microdrive from BestBuy for $149.99 - $50 Rebate - $30. Both rebates ask for the Original UPC but I called (twice) and both times they said that Rebate Offer #05-98010 will accept a copy. Unfortunately that is for the higher amount rebate($50). I guess there is some risk but both times I got the same answer.
If you buy it in the store (B&M) you can use a 10% coupon that is floating around the internet. Basically it saved me TAX and a bit more..
I tried in in my 5D and it worked out of the box. No reformatting needed.
Noticed some slowness is certain functions but for some people (like me) it's not a big deal.
With 4GB, you get around 331 RAW+JPG shots. Not bad.