What happens when I block someone on Twitter? Do they get notified about the block? Won't they see me in future searches? What's the deal?
When you block a user on Twitter they do not get notified that you have blocked them.
By blocking a user on twitter means that they are not:
Any @replies or mentions that they send will not appear in your mentions tab. (These may appear in searches though)
They will still be able to see your tweets if they navigate to your profile page (the only way to stop this is to make your account protected)
It should be noted that blocked users can still retweet your tweets and any @replies or mentions will still be visible to everyone else - they just don't appear in your timeline.
They will also still be able to see your account via searches - they just won't be able to follow you.