At #6 SF can grab a playmaker, depending on who goes off the board before them they could have: Hawk, Davis, Huff, Ngata, Fergusen may even drop to them.
At #22 they get a LT, Winston Justice may be gone, but Eric Winston and Darryn Colledge might interest them, they may have been eyeing Mankins at 33 last year and they can't be happy with a Bill's castoff at LT.
Further, they could trade out of #6 on draft day if the right offer comes along, for example: with Oakland sitting at #7, teams like Arizona, Minnesota, and maybe even Detroit might consider moving ahead to grab a QB.
As for Denver, This trade moves them back into the third round and positions them nicely in the first three rounds.