Yahoo Pipes launched yesterday to much fanfare (      ) and then immediately went down.
The site now displays nothing but the text, "Our Pipes are clogged! We've called the plumbers!"
Yahoo Pipes does sound pretty cool from what I can tell from the gushing write-ups. I am eager to try it too, though I have to say that crashing immediately after launch under load is not encouraging for those of us who might be interested in building something on top of it.
See also Dare Obasanjo's post, "The Problem with Web Scale: Yahoo! Pipes", for some interesting thoughts on why Yahoo Pipes went down and why it make take quite a bit of effort to unclog it.
See also my previous posts, "Lowered uptime expectations?" and "The folly of ignoring scaling".
Update: I have had a chance to play with Yahoo Pipes now. I think the concept is great and the UI gorgeous, but the actual capabilities currently fall short of what I expected from the other reviews I saw.
It appears that Yahoo Pipes is limited to combining and filtering feeds in a pretty simple way. For example, you can take a feed, then exclude every item in the feed that does not match a keyword string. Or you can combine five feeds, then re-sort them based on publication date.
You cannot rip apart the data in the feed in any complicated way. For example, I was interested in taking all the keywords for all the titles and descriptions in a feed, counting them, then sorting them, truncating to the top keywords, then finally running a Yahoo search against those top keywords that is restricted to a specific website. That is not possible. It is not even possible to take a feed, hook up a content analysis module, then run a Yahoo search against the results of the content analysis, since there seems to be no way to extract the y:content_analysis field from the items.
These more complex features may be added with time but, given the scaling difficulties Yahoo Pipes has had, I suspect I shouldn't hold my breath. For now, it appears Yahoo Pipes is limited to fairly simple combining and filtering of feeds.
Overall, I would say that Yahoo Pipes sure is shiny and pretty, but not that dissimilar from FeedShake, FeedDigest, and other RSS mixing services that are already available. It certainly is not the mashup revolution that some gushingly proclaimed, at least not yet.