It (pbmining) is no longer competitive, a few months ago the price was almost half that cex are now almost equal, besides that you can not trade, not instant payments, time indefinite, etc
I'll rerun the 1 TH/s example with cex.io.
pbmining.com - Cost is 2.9BTC with no other fees, 5 year contract, and 10% referral program
cex.io - Cost is 3.17314BTC + 0.18USD per GH/s per month, and it is possible to liquidate your GH/s at any time
0.18USD * 1000 * 12 = 2,160USD or ~3.7BTC at today's exchange rate for one year of fees.
So cex.io is 3.17314BTC + ~3.7BTC or ~6.87BTC expenditure during the first year of mining.
You can subtract 1-2BTC from the expenditure when selling your GH/s after a year.
Still not a good deal compared to pbmining.