A while back, probably via the uF mailing lists, I came across an interesting article by a chap called Jeremy Keith.
The basic principle of it was that like most of us, he's contributing to lots of different places online, and most of those places were offering a feed of those timestamped activities in the form of RSS or Atom, so he built a page that amalgamated everything in once place.
I loved this idea, so naturally I've nicked it (took me a few months to get around to though). I thought he'd called his a Lifestream, but that may be just my hazy memory because he's just referred to it as 'a life stream' in the copy. I've called mine a Lifestream though, and would be happy to take any responsibility for Yet Another Annoying Web2.0 Phrase, but I'm sure someone's used it before.
My lifestream is on the front page of my site and at the moment is aggregating content from here (LJ), bookmarks from Delicious and my photos from Flickr. It's put together in PHP (using simplexml mainly, for those of you who care) and was surprisingly easy to implement. The only thing that was slightly fiddly was getting photos to display as when they were taken rather than when they were uploaded. I added a bunch of hAtom markup to get a nearly-valid Atom feed fairly easily too.
There are a few limitations, of course. The fact it's all derived from feeds and I'm not storing anything on a permanent basis means that things will 'drop off' the end of the stream as time goes on, but I'm choosing to see that as a benefit rather than a hinderance. It means that I won't bother adding pagination, there'll be one page of 'recent' stuff to look at.
I'm trying to think of more stuff to put on there. I have a YouTube account with just one video in, but I can't seem to see how to get a feed of just one user's videos (anyone?). Last.FM would be nice to have on there, but as Jeremy points out in his post above, their feed disappears if you don't listen to anything for a couple of days so it's a bit lame.
I could concievably add a list of the posts I've made to Google Groups, but that may be a whole can of worms. I'll certainly not be adding links to the nonsense I post on The V.