[I run osdir.com] Just to be clear we're not scraping content nor SEOing to death. We've been running our mailing list archive for almost 8 years.
To quote Matt_Cutts somewhere else in this thread: 'because USENET/mailing lists don't always have a centralized/canonical location on the web, which makes dupe content more of a potential issue. It's not the usual "Website X copied my website" scenario.'
If you dislike us that's cool, but just know we're not showing in your SERPs because of scraping & SEO trickery. A lot of people, maybe not you, really are finding their answer there. There's a lot of solid answers in inboxes.
UI: LOL, yeah, it's a toss up here whether to make it prettier or keep it a bit old school.
Compare for example the Apache archives of CouchDB (http://mail-archives.apache.org/mod_mbox/couchdb-dev/) to Markmail archives (http://couchdb.markmail.org/search/?q). The former is searchable; the other isn't.