Planet aggregators are pretty cool, but many of them are “polluted” by blog posts that have nothing to do with the subject. If I subscribe to a MySQL or Apache feed, I don’t want to read about what the MySQL or Apache devs are having for breakfast. Planet Maemo is an example of an aggregator that works well. It still has the occasional off-topic posts, but thanks to tag-specific feeds, many of the aggregated sources are filtered. It’s a truly powerful way to keep up to date with the devs, while still allowing them room for individual expression.
I guess it’s time for me to start lobbying for a Wikimedia planet aggregator. The additional issue here is language — perhaps we need one for each language, unless there’s an aggregator software that supports multilinguality.