The BFL wait list thread has just under 50TH/s of orders. I think someone else around here claimed that Inaba (or BFL_Josh) said they were closing in on 90TH/s of preorders. The bASIC is closing in in 35TH/s of preorders. The Avalon preorders were around 18TH/s.
For my personal calculations, I'm assuming a 200TH/s network by the end of 2012, and then increasing by 20% per month after that. You can do the math to figure out the rest.
Won't happen unless ASIC devices become extremely cheap, much faster, and the BTC/USD rate increases.
Otherwise, your assumption sets you at 1.7PH/s by the end of 2013. Meaning that sexy Mini Rig a user just purchased for $30,000 would net an epic $870 per month after electricity costs.