Social network datasets I am looking for social network datasets (twitter, friendfeed, facebook, lastfm, etc.) for classification tasks, preferably in arff format. 
My searches via UCI and Google weren't successful so far... any suggestions?
 A: Check out the Stanford large network dataset collection: SNAP.
A: *

*A huge twitter dataset that includes followers, not just tweets

*large collection of twitter datasets here
A: A large index of facebook pages was created and is available as a torrent (It is ~2.8Gb) http://btjunkie.org/torrent/Facebook-directory-personal-details-for-100-million-users/3979e54c73099d291605e7579b90838c2cd86a8e9575
Twitter datasets are tagged on Infochimps: http://infochimps.com/tags/twitter
A lastfm dataset is available at http://mtg.upf.edu/node/1671
A: visit the Max Planck institute. They have also collected several datasets for OSNs.
A: Just found this: 476 million Twitter tweets (via @yarapavan).
A: We have curated a Twitter dataset for friends of users in 2009 and then in 2009. You can find more information here: http://strict.dista.uninsubria.it/?p=364
A: A good resource for finding datasets is:
/r/datasets on Reddit.
A quick glance at that page reveals this source, which might contain something useful for you.
A: Check out kaggle.com , they have some contests about social networks and they give out datasets. 
Also, Stanford's SNAP is a great resource. And it has research works to boot.
A: Facebook social graph, application installations and Last.fm users, events, groups at
http://odysseas.calit2.uci.edu/research/
Two datasets (collected April-May 2009) which contain representative samples of ~1 million users Facebook-wide, with a few annotated properties: for each sampled user,  the friend list, privacy settings, and network membership are included. A third dataset ( collected Feb 2008) includes a bipartite graph that represents application installations by Facebook users. A fourth dataset with Daily Active Users and application installations over 6 months (collected Sept 2007-Feb 2008). A fifth dataset that includes a representative sample of Last.fm users obtained using multigraph sampling (collected July 2010).
A: This paper uses a facebook dataset that is available here. Here is the description from the authors:

The data includes the complete set of nodes and links (and some
  demographic information) from 100 US colleges and universities from a
  single-time snapshot in September 2005.

