I've been wondering when the Lion and 64 bit issues would appear here.
😉
Of course it is also worth inventorying your Mac to see what other software (besides pre-10 versions of AC) you have that are non-Intel programs (PPC).
For some, this might be a stumbling block for upgrading to Lion (at least right away).
You can see which running processes are Power PC (PPC) by launching Activity Monitor and sorting the column called "Kind" - which will then group your Intel, Intel 64 bit and Power PC apps.
This will only list running apps, though. You might want to go through everything in your Applications and Utilities folder to inspect their type. For example, Microsoft Office 2004 apps are all PPC. File Info will show these as simply "Application" - as opposed to "Universal" or "Intel" which is what you want to see for migrating to Lion.
Caution: you may have services on your Mac that are located elsewhere and will be hard to track down to determine if they are PPC code. For example, preference panel items or drivers for (older) printers and other hardware or services. At some point before Lion arrives - maybe even now? - I would expect a 3rd party to have some kind of scanning software that would list all of these things for you to make it easier to decide if you can safely switch to Lion without losing some current functionality.
An option that OS X makes easy is to retain your Snow Leopard (or earlier) OS as a boot volume on a separate drive (even an external drive) or a partition of an existing drive. Then, you can at least restart your Mac with the older OS if you need to run an older PPC program. This cloning is done in Disk Manager (and/or with 3rd party programs like Carbon Copy Cloner, Chronosync, etc).
I would always recommend creating a clone of your boot disk before upgrading to a new version of OS X, "just in case".
Even with such an alternative boot volume which could still let you run old versions, it is worth following Greg's advice and converting all files that are in version 6 or earlier format.
🙂
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB