I think users are all on various levels. A month ago I worked for a financial group and they were using 2003. Most of my IT groups are using 2010. I also have many on 2007 in various lines of business. Manufacturing is also slow adaptors but I just finished a proposal to upgrade a manufactor from 2003 to 2010.
Look at the capabilities and functions you need to create your schedules. Many feel what they have is enough capabilities in the older levels and don’t upgrade. 2003 has not been supported for years and support for 2007 will go away by the end of 2012. Another new version is on the horizon which you should be hearing about this summer. One thing I look at is if you have other people feeding you schedules and they are on different levels this will cause a problem. Don’t try to bounce around between levels – this is the best way to corrupt files.