Tags should be a good cue to tell us if a blog post should be read or skipped. I find puzzling that most (all?) feed readers just ignore tags. Surprisingly enough, I could not find any feed decorator.
Yahoo! Pipes to the rescue: after some copy'n'paste, a pipe that decorates feeds appending to every post title its categories (for atom and rss 2 feeds), and also adds the tags to the top of the post: http://pipes.yahoo.com/xverges/tagsintitle
This one does the same, but also adds the results from Yahoo! Term Extraction to the top of the post. I just cooked it, so I am not really sure if the list of terms is a useful addition: http://pipes.yahoo.com/xverges/tagsandtermextraction
Annoying side effects: the feed name, url and description become those of the pipe, so a bit of manual work is required after subscribing to a feed. I hope they fix it...