baltwo wrote:
You need to be booted into an OS X volume to run the installer.
Yes, that's what I did this morning. Usually I do a clean installation (by that I mean erase the HD to scour out glitches, of which there were many in the two Lions) but this time, forgetfully, I just ran the installer downloaded from the App Store. All my emails, desktop, applications (including Adobe ones), utilities, documents, pictures, iPhoto and its photos, music, every single thing were preserved. Saved a great amount of re-installing all that. Hopefully, my mouse problems will have been left behind but I'm not optimistic.
A very few utilities don't work, including Roxio Toast which has been sold to Corel who say it will be upgraded "in a few weeks".