Sam Ruby has whipped up a proto-aggregator pragmatically named wx3pa (for wxPython 3-paned aggregator). I’m not linking to it so you’ll use it (because it is really raw). I’m linking to it as an example of the cumulative power of many people writing many small chunks of code that can be built upon by others.
Python provides the language and basic infrastructure, wxPython provides the UI toolbox. Mark Pilgrim provided the RSS parser, and Sam only had to write 107 lines of code to pull it all together. Granted, it doesn’t do much yet, but it is a full-fledged GUI application that reads and aggregates RSS feeds.