A LOT of companies are going to be in the mixed versions of SQL Server boat. I know of many myself.

I think going forward over the next 10 years this is only going to get worse. Reason I say that is as more SQL Servers pop up and more become critical systems the more time and $$ it is going to take to upgrade them all. Pile on top of that tighening IT budgets and very quick turnaround from Microsoft on new versions too.

5 years ago we only had about 120 SQL Server DBS, now we are about 300 and within 2 years we will be at 500.