In Sublime Text 2 it was possible to comment out a line or a block of lines with Ctrl+/ and Ctrl+Shift+/. According t
On a standard US QWERTY keyboard, as used in Australia where Sublime Text is made, / is readily available:

This is not the case with many other keyboards. Take for example the German QWERTZ keyboard. One needs to hit SHIFT+7 to get a /. This is why commenting does not work properly on these keyboards.

Changing the user keybindings to those listed below, will work for the German QWERTZ keyboard.
{ "keys": ["ctrl+7"], "command": "toggle_comment", "args": { "block": false } },
{ "keys": ["ctrl+shift+7"], "command": "toggle_comment", "args": { "block": true } }
If the problems are occurring with still a different keyboard layout, change the keybindings accordingly.