[billybob]

"What I'd really like is a single online notification service..."

Everything you say about this sounds exactly like hosted email to me. How is it different?

To me, the problem with email is the time it takes to manage it: filter, mark as read, etc. Gmail filters help with this, but it's still work. But I can't see how any notification system could know how I want things filtered without me telling it.

[mseebach]

It would be nice if the community would agree on a simple header that indicates "notification" so it's easier to filter automatically.

[sp332]

You can use address tags to sign up for notifications. https://en.wikipedia.org/wiki/Email_address#Address_tags E.g. if your email is [e-mail] you can sign up for bugfix notifications as [e-mail] which makes inbox filtering much, much easier.

[spc476]

There are three currently defined headers that I can think of: Subject, Comments and Keywords. Personally, I think I would pick Keywords, but that's me.