<p>Have you used <a href="http://pipes.yahoo.com/pipes/" rel="nofollow noreferrer">pipes.yahoo.com</a> to quickly and easily do... anything? I've recently created a quick <a href="http://pipes.yahoo.com/kooshmoose/stackoverflow_merge" rel="nofollow noreferrer">mashup of StackOverflow tags</a> (<a href="http://pipes.yahoo.com/pipes/pipe.run?_id=NIlbqD_E3RGfAAUWpgt1Yg&amp;_render=rss" rel="nofollow noreferrer">via rss</a>) so that I can browse through new questions in fields I like to follow.</p>

<p>This has been around for some time, but I've just recently revisited it and I'm completely impressed with it's ease of use. It's almost to the point where I could set up a pipe and then give a client privileges to go in and edit feed sources... and I didn't have to write more than a few lines of code.</p>

<p>So, what other practical uses can you think of for pipes?</p>

It's nice for aggregating feeds, yes, but the other handy thing to do is filtering the feeds. A while back, I created a feed for Digg (before Digg fell into the Fark pit of dispair). I didn't care about the overwhelming Apple and Ubuntu news, so I filtered those keywords out of Technology, which I then combined with Science and World & Business feeds.
Anyway, you can do a lot more than just combine things. If you wanted to be smart about it,  you could set up per-subfeed and whole-feed filters to give granular or over-arching filtering abilities as the news changes and you get bored with one topic or another.