I had to disable BLC on all the websites I manage after upgrading to WP3.5 a few days after it was released. Within a few days after upgrading, my hosting service notified me that I was running out of disk space on most of my reseller account. It turns out that BLC was creating error messages in the errors.log file in the root directory and in wp-admin so I disabled BLC and one other plugin that I use everywhere because neither one of them were compatible with 3.5. (Note to self: Wait a few days after a WP update is released and then update only one or two websites. Monitor the error logs and see which plugins are not compatible and disable them until they are updated.)
Apparently, I missed one of the websites where I intended to disable BLC and delete the monster error files because I got a warning this morning from my hosting service that I was running out of space again on one of my reseller accounts where there is only one active website. I couldn't even login to the website until I deleted the almost 4GB error file in the root directory using FTP. The wp-admin folder had a smaller (3MB) error file so I downloaded it before I deleted it. When I opened it with a text editor (after adding the extension ".txt"), it was full of BLC error messages. Don't activate this plugin until it is truly compatible with WP 3.5.