I am a long time user of Sibelius 4 and a software engineer. When I installed Sibelius 5 I had nothing but problems. The installation was not very well integrated: there was a .net upgrade which had to be run separately. Plus it was suggested that files should be copied from Sibelius 4 to Sibelius 5. Later the installation guide suggest that these files may not work because of software changes. Since the job of an installation program is to copy and install the correct files, one gets the impression that the installer was very hastily done.

The principle flaw was the removal of means to edit sound set plus no guide on how to create these in the new XML format. So if you were using an external synth, (I'm using Motif Rack) suddenly you old work is now unplayable. Tech support has offered the ususal banality of a fix will be ready "Real Soon, Now." Much of the functionality in the play menu is greyed out or unresponsive. (The manual only mentions that menus have been 'removed' but offers no recourse as how to replace this functionality).

My recommendation is to wait six months to a year and look for positive reviews before buying this 'upgrade'.