What arts organizations have built solid online communities using social media that engage people and may also have lead to fundraising impacts?
What arts organizations have used social media to attract gen x and gen y to their programs?

Please provide a link and if you have time for a quick answer to the question.

Art Tribes Network ~ http://www.arttribesnetwork.com

The Film Society of Lincoln Center -- we present films year-round, as well as the New York Film Festival. Over the course of a little more than a year, we've built a stronger online "fan" base via a blog, Facebook and Twitter (@filmlinc). One way we tried to reach a younger audience was instituting the "New Voices" campaign, which was an initiative to get younger people blogging about our films. An introduction is here: http://filmlinc.wordpress.com/2009/03/11/introducing-the-filmlinc-blogs-2009-new-voices/
And all the "New Voices" materials is here: http://filmlinc.wordpress.com/category/new-voices/

The San Francisco Symphony has launched a ning community which has a strong following. They are experimenting with contests, badges, and other activities to engage their audiences. (not sure about fundraising impacts though.)
http://community.sfsymphony.org/ (e.g. Smule iphone app game contest to win tkts to opening night.)

New York Philharmonic is doing cool stuff on Facebook, integrating cross-platform and on-line off-line. For example, photo contest at Summer Parks concerts, uploaded to Flickr, then winners announced on Facebook = tkts to concerts. Other contest/activities, write short paragraph about first experiences with Mahler, or be on of the first to find out what Mahler wrote in his score on pg 9.... these link to their hi-res online score on home website, and tie in with Mahler concerts and release of new Mahler recordings. - Good example of use of notes page for these longer shelf-life events. (not sure about fundraising impacts though.)

You are up on Brooklyn Museum's 1st Fans ? http://www.brooklynmuseum.org/join/1stfans/ Organized through twitter, with successful on-site events. To read more about its conception read Will Cary's Blog post from Dec 2008

The Mattress Factory in Pittsburgh continues to experiment with innovative ways to connect with its audience through social media collectively calling these initiatives Friendship 2.0.

Feel free to edit us out, because we're tiny, and I'm not sure we're to community yet, but our use of facebook has been successful for us, as well as our e-newsletter strategy. We're River Arts in Morrisville, VT. Twitter less so because in Northern Vermont the demographic is still catching up to the tech end of things. www.RiverArtsVT.org