I don't really remember to be honest, I'm always on the prowl for new shortcuts (I rarely touch the mouse. Also, get Vimium for Chrome.) but it changed how I interact with OS X pretty significantly after I found it.
It is nice, but I sometimes wish that Safari or Chrome tabs would cycle with that combination, rather than the control + tab sequence as then it would all be a bit more similar.
FYI: You can also cycle tabs with Command+Option+Left and Command+Option+Right and Command+[1, 2, 3, etc, with 9 always selecting the right-most tab] in the case of Chrome.
With Safari, you can do Command+Shift+[ and ]
Command shift [ ] works with almost everything that has tabs including safari, chrome, terminal, Xcode and sublime. (those are the ones I use it with).