I think that the mandatory upgrade is overrated. I am still using Acrobat 6.0 and often get a warning that the document I am opening is not compatible with the version of Acrobat I am using. But it is very seldom that I actually find a problem viewing a document. The only one that comes to mind are the data sheets from Silicon Blue. Some of those actually can not be viewed using Acrobat 6.0.
The reason I am using Acrobat 6.0 to view PDF files is because Adobe makes Reader and Acrobat incompatible. If you have Acrobat open and try to open Reader, it simply switches context to Acrobat and likewise if Reader is open and you try to open Acrobat, it simply switches to Reader. So rather than try to fight the tools, I just do all my viewing with Acrobat. Since I don't want to continue to pay for the upgrades, I am still using 6.0 which works fine for 99.9% of the docs I want to read (except for Silicon Blue :-(