I installed Little Snitch a couple of years ago, and I thought it was a neat tool. However, after upgrading from 3.6 to 3.8, my computer was completely messed up.
It wouldn't boot (it would chime, but not boot), and most regular boot commands (like shift, c, cmd-r and so on) didn't seem to take effect. I started it in Firewire Target mode, and I couldn't see the system drive.
In the end, I had to remove the system drive from the Mac, put it in an enclosure, mount it on another Mac, remove /Library/Extensions/LittleSnitch.kext, and then put the drive back. At this point it booted, and I proceeded to remove all other traces of Little Snitch.
So, four stars for the basic functionality becomes a single star, given the tendency to brick computers.
(For what it's worth, I think the problem was that Little Snitch was trying to run at an earlier stage than before, during the actual boot step. I'm not sure if the upgrade itself did this, or if I changed a preference in association with the upgrade, but either way, this is just too risky for me. I'm going to use Hands Off! for these purposes going forward.)