VentureBeat has an article covering their launch which you should probably check out. Here is the video from their website:
The chief scientist at the company is Barry Smyth, a professor at the University College Dublin.
It's a bit early for a full review, but I tried it out and it seems promising. I have some privacy concerns about browser toolbars that save and share my search history, especially when the service is oriented towards public sharing of the information.
HeyStaks reminds me of the failed Yahoo! Search Pad, but with a more social focus, and it works across search engines. I hope it has better luck.
I would like to see the service evolve to have more collaboration in the search beyond saving and sharing results. For example some deeper integration that Gene Golovchinsky, Jeremy Pickens, and others have been advocating. See their paper, Algorithmic mediation for collaborative exploratory search which won the best paper award at SIGIR 2008.
My congratulations to Heystaks on the launch. I look forward to Chome and Android apps versions that I hope will be soon to follow.