Jean-Bob is right in his recent comment in one of the current feedbacks concerning the current client. There are many problems, and they are in many feedbacks.

There are many, and some older ones have been revived to connect older problems with current ones. Here is a list of the types of feedbacks that have been filed.

Puzzle 670 specific -

Known crash filed by dev: Puzzle 670 crashes when 'Show expected residue burial' is enabled (http://fold.it/portal/node/994336)

670 crash in disulfide scoring function - http://fold.it/portal/node/994358

670 is too laggy to play - http://fold.it/portal/node/994347

Older feedback on returning bugs in 670:

crash when wiggling on puzzle 627 with lots of cysteines using devprev - http://fold.it/portal/node/993469

Mutate Sidechains feature takes too long to stop - https://fold.it/portal/node/991306

Other feedbacks that are possibly client specific, but perhaps associated with 670 and the new filter:

2013-01-15-53170-win_x86-devprev memoryleak - http://fold.it/portal/node/994359

There are also many people in global and in my group who have clients crashing frequently (especially overnight) since the 1-16 update - that is happening in 670 and 669 that I'm hearing.

Please leave a comment in one of the feedbacks noted here, or a comment in this feedback if you are having any issues. The more info we can give the devs, the more likely we will get fixes, or a rollback if warranted.