Would you expect to be able to open a drawing created in r2007 with r2008 without any issues? I had a Final Plat fully annotated in C3D 2007 that was put on hold until an adjoining phase of the development was completed. While this phase was being completed, our office upgraded to C3D 2008 to take advantage of features that were either new or fixed and an overall increase in stability. When it was time to finish off the Final Plat of the earlier phase, the base drawing had been converted to 2008 and at least 2 of every 3 line labels were missing and none of the curve labels had survived in usable format.
It is quite common for large residential development projects to span several years, and often the same basic information is being used in planning stages for one phase, early design in another, finishing the approval process for a different phase while being staked for construction for a phase nearing completion.
With the current release cycle and having basic elements not able to carry forward much less back to previous releases, there is a significant interoperability problem with at least this vertical application.