This is awesome but what is the motivation behind this? Why do you care to set up a server and pay for the (minimal) bandwidth that is needed for this service? Is this purely an act of goodwill? Do you hope that this will gain traction so that you can start charging for the service? Are you secretly harvesting clusters of IP addresses of HN readers?
Maybe one day if there are a lot of users I'll implement paid accounts with more than 10 alerts and history dashboard. But most likely it will never gain enough traction for that, in which case it's no problem, since I have 6 tiny servers for different activities and this only uses 2 of the with minimal resources (it's just ping). It will just sit there alerting me and some others when something goes down.