You can't get sneak attack benefits when the target benefits from concealment.
When blinking, your target gets concealment on every attack you make! (unless you can both see invisible and strike incorporeal).
Blink spell description, third paragraph:
"Physical attacks suffer a 50% miss chance, ... [skip to the relevant bit]... If the attack is capable of striking ethereal or incorporeal creatures, the miss chance is only 20% (for one-half concealment)."
Since the lesser penalty (20%) is half concealment, the 50% penalty is by extension full concelment. Thus, while blinking, you can't strike accurately enough to use sneak attacks.
(This ruling came in handy in my game where a rogue spotted the Ring of Blinking would allow him to make every attack he EVER did a Sneak Attack.)