I used to use Readability to deal with problematic web sites, but I switched to Clearly after encountering a number of web sites that Readability had problems with (not rendering all the content). I didn't know about Readability's feature of exporting a page as ePub. I may have to give readability another try.
My primary use case, though, is in organizing content I find online related to a research project -- the ability to tag, star, and archive content is particularly useful. Though I do wish the management and search tools were more powerful.