if you were looking at it from the same level as the peoples heads though, they will be seeing the stage fine, it is only really if you are really far back that it blocks your view but then you wouldn't see much from back there anyway, i camp opposite the pyramid stage and i go into the crowd and only ever to about half way down and i can't say i have ever really had too much of a problem or certainly never thought it was because of the flags. As long as they don't become forms of advertising i like them and think it makes the festival unique