This is only a quickly compiled list, but here is a table of some of the major social media tools being used by the top US magazines as listed by their 2006 circulation:

2006 Rank
Magazine
Main Page Feed
Message Boards
Twitter
Facebook
Myspqce
Blogs
Online Community
Other Notes

1
AARP

√

√
Photo sharing, journals, video podcast

2
Reader’s Digest
√

√ (1700 followers)
√ (1500 fans)

Several Channels
√ Via Gather.com
Central site links and portal [...]

Here’s a quick collection of lists of museums active in the social media space.
Museums on Twitter (click here to download the full spreadsheet):

Museums on Twitter
name
followers

brooklynmuseum
brooklynmuseum
12679

thewomensmuseum
The Women’s Museum
1451

sciencemuseum
Science Museum
1373

exploratorium
The Exploratorium
1233

gr_art_museum
GR_Art_Museum
794

knoxart
Knoxville Museum Art
728

woodenboat
Spaulding Center
664

mattressfactory
Jeffrey @ the MF
638

eastmanhouse
EastmanHouse
596

atamnh
AMNH
566

grmuseum
Grand Rapids Museum
560

24_hour_museum
24 Hour Museum
524

thefranklin
thefranklin
514

henryartgallery
Henry Art Gallery
507

rubinmuseum
Rubin Museum of Art
497

cincycac
Contemporary Arts
469

americanart
americanart
416

huntermuseum
Hunter Museum
379

asuartmuseum
Diane Wallace
349

21stcenturyabe
21stCenturyAbe
306

asianartmuseum
Asian Art Museum
291

arc_appalachia
Arc of Appalachia
208

mfsm
MFSM
168

fortsmithcvb
FortSmith CVB
136

sciencemuseummn
sciencemuseummn
108

chemheritage
chemheritage
90

edventure
EdVenture
83

cyberville
Cyberville
59

artglassmuseum
Bergstrom-Mahler Msm
39

And, compiled [...]