What will happen if i don't backup my Iphone files after updating my Iphone?

So i had an iphone 4 and i tried updating it to IOS 5.1 and after updating it told me to backup my files so i backed up and it is taking forever to back up it has been like an hour the bar did not even move it moved a little from the start. Can i chose not to backup will anything happen if i don't back up?
I currently used 29.1 gb space in my iphone

Added (1). I only have one place to store my stuff
382 GB of 451 GB used

Well my friend, Your iphone carries a load of apps and etc. Have patience it may take 2 to 3 hours appox, but I worry your PC or your notebook has less memory,
For faster backup, click on preferances, change your storing folder from folder "document C" to other drive for example Drive "E" OR "G". This will make your backup in half or an hour!