[rrowland]

Keep in mind that your return is based on the current net hash rate of all mining computers, everywhere. Combined with the 6+ month wait time, you can buy a $20,000 rig that would mine you $500/day today but by the time you get it the hash rate will have risen so high that you'll be lucky to out-mine the cost of your power consumption.

I wouldn't be surprised if these companies were using each rig for a couple months in their prime before shipping them out.

[wmf]

...using each rig for a couple months before shipping them out.

Looking at the global hash rate it's clear that this is not happening. (Before anyone asks, you cannot hide mining.) http://bitcoin.sipa.be/