It's been almost 3 weeks since I co-invested in a mining rig and I'd like to thank everyone here for the help they offered. Thanks guys, it was awesome fun.
Since buying the rig (2x6990) difficulty has doubled and price is down by some 25%
So is it still worth it? IMHO definitely.
What we've seen in the price fluctuations is actually still relatively mild compared to what things could have been; imagine a single high power real world trader entering BTC in earnest. The short term fluctuations someone like that could create would dwarf even the recent exchange hackings. So I don't see the price as having come down so much as having simply osculated. I still believe BTC has a shot at replacing most of the fiat supply and that would imply a cost reasonable upwards of $15
Even though our mining is currently bringing in less than 2 BTC per day, if bitcoin succeeds even mildly we will look back at today's mining data and call them "the good old days" when difficulty was low and returns were (in retrospect and with the future price) incredible.
So I'm going to keep mining and holding. I still think it is going to be a profitable racket to get into for quite a few months.
Just my 2 mBTC