Migration Assistant

I got similar symptoms when my hard disk was failing. More and more sectors fail and data gets moved to good sectors until eventually something critical gets corrupted and you are so glad you have bootable backup on an external disk or that new computer itself. You can use Carbon Copy Cloner or the like to make a clone.

Should it be too late for this strategy, you may need to rescue your own data, photos etc to another disk. It may even be prefereble to install your apps from their source, but you need the keys handy.

If you can, use Setup Assistant at the first boot of the new computer, to transfer your user account. Using Migration Assistant later makes another new account and leads to difficulties accessing original data from other sources.

Apple Hardware Test doesn't catch everything, so even if it doesn't find a problem, you could have one.

Apple Hardware Test

The migration shouldn't be a problem unless some of the files are corrupt. I second using Setup Assistant.

Note that if the disk is failing, it may be better to stop making any more backups, in case further corruption gets carried across to the backup copy too.

That is debatable. I do not have all my original disks for my apps, so took the risk of transferring my user account. The theory is that data gets moved out of bad sectors and Carbon Copy Cloner (CCC) gives an error message when it sees corrupted data but then leaves the "last good" data in place. So nothing bad should get across, in theory. I have not had any repercussions myself, and a full clean install takes hours, with numerous visits to manufacturer's websites to get updates to apps, drivers et al.

There is a risk attached. Did CCC throw up any error messages? If so, make a careful note of them, so you know what may need replacing..

• it sounds like my safest option is just to start from scratch and reinstall everything.

That is the safest option.

If you plan to use CCC I suggest you first check out the documentation:

http://www.bombich.com/software/docs/ccc/en.lproj/advanced-strategies/the-clonin g-coach-expert-advice-for-common-error-conditions.html

On consideration I must agree with Eustace. Apart from anything else, there are large differences between SL and ML, so you would need to get updates to all your apps and drivers in any case.