I looked at all the sites although the majority held little interest for me.
That said, I will keep the account. I think that once I get used how the site works and what types of content one is likely to find there, that the subreads could be a resource for information that might be otherwise hard to find for professional and/or personal interests.
Libraries could use the tutorial mentioned in Thing 66, to show patrons or groups (e.g. book groups, genealogists, quilters etc.) how to set up subreddits of interest and while doing so, talk a little bit about how to evaluate information. found on the web.
DIGGI found Digg visually appealing and a place to "graze" but since I've little interest in or need for either a Twitter or Facebook account, I didn't create an account, Still, I imagine I'll return to Digg once in awhile.
Digg could easily be recommended to patrons as a current-events site. On a more whimsical note, could see choosing a story found on Digg, as the basis for planning promotional/outreach events, reading lists (both fiction and non-fiction) Book and/or discussion groups might find Digg a useful resource.