I tried updating a #! (Wheezy) system to Debian Jessie a while back. Massive breakage.
No really major dramas. Run cb-printers before the upgrade to Jessie. Icons do screw up a bit, but easily fixed by installing some similar Gnome 3 icon themes. I'm using cb-waldorf-xoraxiom and "Grey-Icons" at the moment. Everything else seems to work fine.
I really like the #! Openbox experience and have yet to find anything quite like it. I did try Archbang during this re-build process, but wasn't convinced on first viewing. I know I could just install Debian and Openbox myself, but then have to spend a lot of extra time setting up menus, conky etc.
I'll miss #!, as I've really enjoyed it over the last three years. I've no reason to install anything else right now, but in six months I suppose I'll go elsewhere.
One problem I've got is black internal borders on some of my menus (e.g. network-manager panel menu), but it doesn't affect me much and I really can't be bothered to read the docs to sort it out. Any ideas?
This was the good thing about Crunchbang: a lightweight debian install that looked good and needed hardly any configuration to work well.
I installed base Jessie from netinstall image with no desktop, then manually installed slim and openbox, and started from there.
It's much cleaner this way