check out a free program called infinitewp
you install the infinitewp client plugin on your blog, which gives u a unique key
you then go to the infinitewp admin (which you install on any of your servers).
add the wp blog, with its unique key
and you’re able to update wordpress and your plugins remotely.
I tried it out, setup 40+ WP blogs, and updated 30+ of them without any problems – WP and plugins.
It also sends me a daily email letting me know if I need to update any plugins or blogs.