Scouts can be used to scout other players castles and also to discover clues during quests.
If a scout is successful he will return with the layout of the castle at that point in time. When you attack another player's castle you can use the View Castle button to view the castle layout only if you have previously scouted or attacked them or if you have been sent a report of a scout/attack on that castle by another player. Remember you will only see the castle layout at the moment it was scouted/attacked, changes made since then will not show up.
No. The success of the scouting mission depends on the number of scouts you send, the level of the defending keep, the number of defensive archers and a bit of luck. 150px|thumb|right|Cancel scouts
Yes, they can be cancelled.
If you finish research after the scouts have started moving on the map, the research will not affect them.