This leads me to think that they are just trying to control the ways you put funds into and out of gox.
My guess, assuming seizure remains limited to that one Dwolla account, is that there is some specific transaction that flowed through Dwolla to Gox that they have an interest in which likely was sourced from "illicit" funds.
If Bitcoin itself was the target, then there would have been a coordinated effort to shut down all entry points, as has been the case in the past with, for instance, coordinated MPAA DNS takedowns.
Look at it from the perspective of someone planning an operation. You would not give advance notice by executing it piecemeal. You would liquidate all targets at once. So I think this is a one-off and possibly a buying opportunity as people overreact to the uncertainty.
Nevertheless, it also should be taken seriously as a dry run because, if someday a coordinated attack on Bitcoin does come, it will likely have similar characteristics, except executed simultaneously at all key chokepoints worldwide including, guaranteed, a joint operation with Japanese authorities in Tokyo to shut down Gox itself.