A seventh-round choice one year generally equates to a sixth-rounder the next year.
Tony Grossi's note about the Browns acquiring Seneca Wallace for a conditional 2011 seventh-round choice shows how little the Seahawks valued Wallace as part of their plans. The pick could become a sixth-rounder depending upon how Wallace produces in 2010. Best-case scenario, then, Seattle received the equivalent of a 2010 seventh-rounder.
That's not much, but it beats what Seattle would have gotten for releasing a player who struggled in a new system last season and would have been learning another one in Seattle for 2010.