Got blog? Will ping.
http://googleblog.blogspot.com/2006/10/got-blog-will-ping.html

Interesting that they've decided to do this themselves instead of relying on the 100s of other PING services out there. For now they're saying, "We'll continue to monitor other pinging services and will contribute change notifications to the community." but I wonder if they'll phase out support for those at some point...

And for those too lazy to read...

Here's the form to do it manually:
http://blogsearch.google.com/ping

Here's the API:
http://www.google.com/help/blogsearch/pinging_API.html

<< Google publishes Blog Search ping activity as an XML file to:
http://blogsearch.google.com/changes.xml >>

I'm sure that could be useful for something, although I've not seen it change yet and it doesn't seem to list many blogs...

Edit – I've just seen it update. It seems to do it every five minutes.

Edit 2 – Actually, it does it more often than that. Maybe it just wasn't getting many pings since it's only just been released.

I saw a similar kind of "just updated XML" on Blogger once. Then when I tried to locate it again I didn't find it. This stuff is interesting to do things like "just updated Blogger images" mashups...

Here's Blogger's recently updated XML:
http://www.blogger.com/changes10.xml

And the same thing in HTML:
http://www.blogger.com/changes10.g