Shooting a kudos was something during forum modding (moddingv1) where it would increase the star priority and make it more visible (because maps were sorted by that). Nowday, this system have been removed (since it's no longer possible to use moddingv1) and as been replaced by the hype system in discussion (moddingv2). This act in the same way, but instead of using kudosu, all osu account are given a certain amount of hype per week.
(Also, by that, kudosu are now back to useless)