What machine and how much RAM for starters? Go to About this Mac/More Info, what Model Identifier?

You need to be running Snow Leopard to upgrade. Scratch that, you have the thumb drive, SL not necessary.

Also remember that Lion will not run PPC apps, it doesn't run Rosetta. So you'll need to look at your third party apps and make sure they'll run.

Lion does run faster than Snow Leopard, but only if you have enough RAM.

You can revert back to Snow Leopard if you don't like it but it involves wiping the drive and restoring from a clone of your old system, there is no back grade migration path.

That's off the top of my pointed head, if I think of anything else I'll post.

Edited by Jim_ (07/18/13 02:19 PM)