I do have the same question.
I started with 1.0.19870.4. After 2 months of learning and customisation I was ready to open my shop. I decided to upgrade to 1.1.1 in view of the many new features such as virtual product and bundle product, and of course, many bugs fixing.
I put all my customised files in the local directory, as suggested. I then realised that this doesn’t make sense.
The reason for upgrading, in my opinion, is to take advantage of the new features plus bugs-fixing. I do not see the need to keep my own customised files and let them run in the local directory if those files contain bugs that have been fixed, or, there are enhancement/crucial changes made in those files in the new version. So, I decided to re-do my customisation on 1.1.1.
I suggest if the Magento Team could kindly provide a list of the files that have been changed in the new version compared to the previous version. This way I can see how many of my own customised files are affected in the new version. At least I can estimate the effort/time required to upgrade.
As of now, I am reluctant to upgrade to 1.1.2 in view of the long list of reported issues. I would prefer to wait for 1.1.3, but then I would have no idea the amount of work required to upgrade.
I thank the Magento Team for a wonderful software. I just hope that the ongoing maintenance/upgrade of the software isn’t as painful as it is.
Thank you very much.