How well the tool adheres to the following mashup principles:
Online software that takes minutes or hours to create instead of days and weeks.
Pipes is "an interactive feed aggregator and manipulator. Using Pipes, you can create feeds that are more powerful, useful and relevant".
You need a little reading up on the different components, but quite easy to look at ready-made examples that can give the novice a quick-start into creating personalised web services, ie: aggregator of rss feeds.