Neither company is in the habit of announcing official release dates publicly. Rumor mill has Z68 this week, but like I said, you can already buy the mobo's online.
BD is rumored to be end of Q2-Q3.
Highly doubt BD will perform close to SB. What it will do though is renew competition at the lower end where Phenom II's, even with OCing taken into account, are a poor buy right now above the $100 mark. Could also result in Intel price drops for SB depending on how close the top end BD CPU's get to SB performance.
z68 is a sandy bridge chipset. It combines the H67 chipsets ability to use onboard GPu and quick synch with OC abilities of P67. Throws in SSD caching as well, though I doubt many ppl will use it. Price will be the same as P67 so really no point in not grabbing it.