For those of you who don't know what BB4Win is it stands for Blackbox for window which is a shell replacement for windows explorer which changes the overall look, feel, and performance of windows. It's actually a ported Linux shell and thus it's fairly customizable/tweak friendly plus has a bunch of styles and plugins available for it. Blackbox comes in a few different builds BBLean and Xoblite are both very popular ones I prefer BBLean due to it's emphasis on minimalism and performance. As far as performance goes it lowers memory usage over the standard windows explorer shell a review on shell-shocked quoted about 7-8MB ram usage from blackbox itself and the lost in the box forums claims you save around 10-16MB worth of ram compared to the standard windows explorer shell. It might also save a few cpu/gpu clock cycles as well due to BlackBox's bitmap-less approach for it's styles that are text file based similar to CSS styles. There are also 32 bit and 64 bit builds of available and since it's a Linux port there are builds for that as well aptly named Hackedbox. Anyway here's some links on it if people want to look into it more the very bottom link has a bunch of screen shots of how it looks.
Here's some links on it
http://scrudgeware.org/projects/Hackedbox/ (Linux version)
http://www.boxshots.org/style/ (Screen shots)