Hi Sam, would this hold good to WPMU as well? I figure it is definitely not as up to date as WP.
I tried installing these plugins in bbPress but WordPress doesn’t seem to recognize that I am already logged into bbPress or vice versa.
When I look at the cookies, WPMU has just wordpresspass & wordpressuser set. The bbPress cookies look like wordpressuser_2c7… & wordpresspass_2c7..
This is with the two plugins installed and made to load with the underscore.
I will appreciate any help. Thanks!
macbis, after 8 months since you posted I kept hitting this when I tried to install bbPress in a subdirectory inside WPMU. Your fix worked just dandy! Thank you.. now on to doing the rest of the integration. 
