Google Alerts are seriously one of the best things I started doing in recent memory:
The product works like this:
You figure out what you want to be sent updates on, eg. an ongoing news story. And then you construct a plain old google query which returns things related to what you’re looking for. As soon as new results show up for that search, Google tells you about them. This feature lets you create arbitrary news feeds on whatever subject you want out of googles indexing. It’s amazing and lets you keep up on a huge number of topics and people in a way that just wouldn’t be possible otherwise.
Scalability - I don’t know if there’s a limit to how many Google Alerts you can have, but if there is I haven’t reached it yet. I can keep track of as many obscure niche topics as I want just by providing google with a search that would show me stuff about them.
Fire and Forget - News might only come out on a subject once every three months, if I had to go visit google every day to search for it I’d get bored fairly quickly. It’d be a waste of my time. With this I can set up the trigger and let the fish fly into my inbox.
Customizability - It really doesn’t get much better than this in terms of being able to flexibly coax the tool into doing new things the designers probably hadn’t expected. You can also take your returned pages by email or RSS.
I wouldn’t mind this being something our search feature does if we get big enough.