I bought the 500GB WD from Costco and it died within a week. We had a power outage and that killed it. My other LaCie 250GB and WD 250GB were fine, but the Costco one (which is actually a higher model than my other WD) was just dead, no warning.
Now, this could happen with any HD, which is why you should always have more than one back up plan, but I must admit it gave me pause, and I just got my money back and didn't replace that EHD. I'm not saying you shouldn't buy it, but I thought I should mention it. My LaCie has hit the floor hard from table height, it's been through multiple major power outages and is still going strong. My other WD hasn't had a hard fall, but it's been through all sorts of power outages with no issues.
I think I'm going to pick up the LaCie 1TB Raid 0 configured EHD (it's actually 2 500GB drives) on sale at Best Buy this week and use that as the EHD I work off of, and make my old LaCie the one my Mac Time Machine backs up to.