Mu Folder not used anymore?

Am I right in saying that it is not necessary to place MU plugins in the mu folder anymore?

We started with WPMS in Spring of 2011 when this was needed. We'd like to use this plugin: http://wordpress.org/extend/plugins/si-captcha-for-wordpress/

But I just want to make sure it is placed in the right folder.

Thanks!

DPR