As exciting as SQL Server 2012 is, with its multitude of new features, it’s not always possible to upgrade right away.  Here are some reasons that may cause you to delay your upgrade:

Training – Your developers and dba’s will need to learn the new features of SQL Server 2012.  Finding the time for them to carve out and take away from their other tasks could take a while

Licensing – You will have to spend money to purchase new licenses.  For earlier SQL Server versions, you bought one license per physical processor regardless of how many CPU cores it had.  If you chose your server hardware smartly, you could buy eight CPU cores for the cost of one SQL Server license and save enough in licensing fees to pay for the new server.  To license SQL Server 2012 for that same server, you’ll need eight core licenses.  The new core license fees are less than the previous per-CPU fees, but, if you do the math, Microsoft has conspicuously increased SQL Server’s price

New server purchases – Usually the purchase of a new server or two is required in order to test out SQL Server 2012, and then more servers to upgrade just a portion of your databases (since rarely will you upgrade everything at once and you usually don’t want to mix two versions of SQL Server on the same server)

Certification by hosting company – Many companies are at the mercy of their hosting company to certify the use of SQL Server 2012 before it can be installed into production

Certification by 3rd-party applications – Chances are you are running at least one large application from a 3rd-party, and you can’t upgrade the databases it uses to SQL Server 2012 until the 3rd-party gives the ok

Testing – Of course you must test all the databases on the new version.  This takes time and you may be too busy to get to it

More info:

When Will You Upgrade to SQL Server 2012?