I think that we are currently in a huge difficulty spike, only because the ASICs are brand new and they are boosting the network. However, this boost won't last. I predict that the huge difficulty jumps (30-40% per increase) will continue as long as the new ASICs are shipping, but once they are out the network will settle back down to the regular ~10% increase per block, after the huge hype of "OMG ASICS" dies down and the network restabilizes. So, lets try to predict what we will get to, based on the ASIC companies.
Avalon 150T (500K chips on order) + about 80-100T in batch 1-3 miners (not sure whether chips are included in there twice).
BFL - who knows? say 250T (max would be 500T)
ASICMINER could bring another 200T
KNCMINER - say 150T for first 500 (mix n match of 175 and 350GH/s miners).
Bitfury & Others, who knows? say 500T
Lots of these are guesses, so I vote that we work together here and see what we can come up with, based on the hardware, not just running numbers and exponential difficulty charts.
I'll start with BFL. According to http://bfl.ptz.ro/, BFL has 392 terahashes that are ordered, and they claim (though we all know how good BFL claims are) that they will catch up with all their orders within 90 days. That brings us to mid september, so lets add 400 Thashes to the network in Sept and see what the difficulty will be.
The current hashrate is 144 Thashes, add 400 brings us to 544, which is a 3.78x increase. So, increase the difficulty by 3.78, and we have a predicted difficulty mid september of 71.5 million.
Help me out here guys, lets get some real numbers being run! I'll continue research and post as I get it.