Hey there Gardengirl, to answer your question...the time for getting a cane is when you feel you want to get one.
For me, I was still working on base at HQ and had to walk from one end to the other to get in and out.  My limp became worse, the pain from struggling along was more intense and the whole while I considered the problems associated with being an officer, in uniform, with a cane.  You see, the role of an officer (and this really only seems to be true for other officers) is to set an example for their subordinates.  They are discouraged from displaying tattoos, smoking cigarettes, or wearing blue-jeans - one guy was told he couldn't drive a scooter to work because it "wasn't professional"?  Stuff like that.
I was standing in a store shopping with my wife and tried out a cane just for fun...I instantly fell in love with it and took one home.
My advice would be, to hell with other people - if you use words like "hobble" or "limp" to describe your movements then you are a prime candidate for getting a cane.  
Oh and some people use the term "Pimp-stick" as well...lol
I find it's easier to deal with situations when you have a little advanced warning.
Oh and check out the link in one of the earlier posts in this thread - the one about picking the proper sized cane for yourself.  I found that it was very easy to understand and helpful.  Also, my right arm hurt a bit more for the first couple of weeks until I got used to it.
Take care and LOVE YOUR CANE!
Chris