I'm so far behind the times with Tiger, I'm not sure what to do. I assume if I upgrade to Mountain Lion, then decide I don't like it, I can go back by using the install CD again. Right?
You may not be able to install Lion over Mountain Lion. You might have to erase, install Lion, then restore your user files.
Or more simply, restore from a backup that you made before upgrading to Mountain Lion. Time Machine has no qualms about restoring to a previous version of the OS, and once the OS is rolled back you can use Time Machine again to restore your documents. That is:
Time A: Start using Time Machine on your spiffy new MBP running Lion.
Interval B: Make new documents.
Time C: Upgrade to Mountain Lion.
Interval D: Make more new documents.
Time E: Decide to go back to Lion.
To do that, boot from the Time Machine disk (bootable since 10.7.2), or from the Recovery HD partition. Do a full disk restore from TM back to Time C, the last TM snapshot before you installed Mountain Lion. Then use TM again to restore just the documents created during D.
If you make a mistake, say by rolling back too far or not far enough, or restoring a document to a Mountain-Lion-only format that your Lion apps can't handle, you still have all your TM snapshots and can try it again. The worst that can happen is that you'll decide to give up on the whole roll-back-to-Lion idea, and just use TM to do a full restore back to Time E. As every Science Fiction writer will tell you, the nice thing about having a Time Machine at your disposal is that no matter how badly you mess things up you can always fix it up with one more trip through time, as long as you don't kill your grandfather / erase the backup disk.
