Two years ago I compared Notifo and Prowl as tools for sending custom push notifications to your mobile devices. I ended up relying on Notifo quite a bit to send me mobile alerts about certain kinds of events that I might not otherwise notice right away - email messages from certain people, some kinds of calls or voicemails at my office, certain messages meant for me in the office chat room, etc.
(You might think all that alerting would get obnoxious, but having these notifications sent to me according to my preferences has meant I'm less likely to obsessively check email or other digital inboxes for something important I might be missing. The good/important stuff gets to me fast, the rest waits for me to view it at my convenience.)
In September 2011, the creator of Notifo announced that he would be shutting down the service. It's continued to mostly work since then without his intervention (a testament to the self-sufficient nature of what he created), but in the last few weeks I've seen increasing errors or delays in getting messages through, so I went in search of alternatives to Notifo.
Today I found Pushover, a really simple but elegantly done service that offers all the features I want.