I read an article written by a professional cruise reviewer where he suggested to book the cabin category that you want because he has never recieved an upgrade into another category and he has sailed on hundreds of cruises.
I have had cabin guarantees and each time we got the bottom of the guaranteed cabin.
My travel agent told me that it is very rare to go from inside to outside, outside to balcony and etc. By saying rare I guess it does happen.
I have also read where people claim to have booked a category M and got the Owner's suite. Some people put 75 cents into a slot machine and hit for hundreds of thousands of dollars. I guess some people are just lucky. I am not one of them.
If an outside or balcony is something that you really want you may want to book it. Otherwise just be happy with what you get and anything else is a bonus.
Good luck. [img]/infopop/emoticons/icon_smile.gif[/img]