I run several WordPress Blogs.

I would like to:

• Write content for different blogs from the same admin section.
• Allow users to on various blogs access to my other blogs with a single sign on.

http://techblog.touchbasic.com/html/single-unified-login-for-multiple-wordpress-2-8-installs-in-subdirectories-using-cookies/

Will this plugin help?

http://wordpress.org/extend/plugins/root-cookie/

How about this one?

http://wordpress.org/extend/plugins/kish-multi/

http://wordpress.org/support/topic/164758

Update: 2012… WP 3.5. It seems that for what I am doing that a WP Multi-site is the way to go.