For this to work, your font also needs to be set to monospace.
If you think about it, lines can't otherwise line up perfectly perfectly.
This answer is detailed at sublime text forum:
http://www.sublimetext.com/forum/viewtopic.php?f=3&p=42052
This answer has links for choosing an appropriate font for your OS,
and gives an answer to an edge case of fonts not lining up.
Another website that lists great monospaced free fonts for programmers. http://hivelogic.com/articles/top-10-programming-fonts
On stackoverflow, see:
Michael Ruth's answer here: How to make ruler always be shown in Sublime text 2?
MattDMo's answer here: What is the default font of Sublime Text?
I have rulers set at the following:
30
50 (git commit message titles should be limited to 50 characters)
72 (git commit message details should be limited to 72 characters)
80 (Windows Command Console Window maxes out at 80 character width)
Other viewing environments that benefit from shorter lines:
github: there is no word wrap when viewing a file online
So, I try to keep .js .md and other files at 70-80 characters.
Windows Console: 80 characters.