Howard Rheingold has been tweeting about cloud bookmarking site, Diigo.com, being offline as of about 7 hours ago: "Not only does Diigo go down the very day I start teaching it, @diigo hasn't tweeted in months and the whole site seems to be gone."
https://twitter.com/hrheingold
Diigo is tweeting that "We're working on restoring access. Pls stay tuned for our tweets for latest update. Sorry for the inconvenience & thanks for your support!" https://twitter.com/diigo
This sucks because many thousands of users (including me) migrated their bookmarks to Diigo after Yahoo abandoned delicious.com.