Common and preferred shareholders won't be outright eliminated, as some had feared. But while the shares will continue to trade, it may for investors be a distinction without much of a difference.
This will likely impact many banks since they hold shares in these companies. Here's an excerpt from today's press release from the FDIC:
The federal banking agencies have been assessing the exposures of banks and thrifts to Fannie Mae and Freddie Mac. The agencies believe that, while many institutions hold common or preferred shares of these two government-sponsored enterprises, a limited number of smaller institutions have holdings that are significant compared to their capital.
Update: I found two good articles discussing how this will affect the banks and depositors. Several banks that hold substantial Fannie Mae and Freddie Mac stock are listed in this Seeking Alpha article. This BestCashCow article makes the case that we'll see higher deposit rates since these losses will increase the banks' need for capital and since banks won't be able to sell mortgages so easily.