Method 1: You can put replay in following folder: "C:\Documents and Settings\<user_name>\My Documents\StarCraft II\Accounts\<ID_of_user>\<ID_of_folder>\Replays\Unsaved\Multiplayer\". After this replay will be available from "Replays" section in game.
Method 2: Click with right button on replay, choose "Open with...", if there is no "StarCraft II" in list of programs, then click on "Choose program..." and find EXE-file StarCraft II.
1) You can download any replay from site.
2) You can comment any replay.
3) You can vote any replay.
4) You can add replay in our database.
1) You can comment on forum.
2) Comments for replays became easier. No need to fill additional forms.
3) "Filters" menu contains "Hide downloaded".
4) All replays, which are added by you, connected to your account.
The most useful is: SC2Gears.