After upgrading from Lubuntu 12.04 to 12.10 I see a lot of repositories disabled in the list of sources.
What should I do?
You have a lot of external repositories enabled. All external repositories are being disabled in the upgrade1 process to avoid conflicts and you were probably warned about this by the upgrade manager.
There's no simple "yes, enable them all" or "no, don't do it" advice to give here. And this is the reason why the upgrade manager left you to fix it manually.
After a successful upgrade, check for the availability of packages for 12.10 in the entries and re-enable them in case you still want to use them2. Make sure to select the right release channel, e.g.
Some external ones with a less specific release channel like
1 Irrelevant whether repositories providing packages for the new release. You'll have to fix it up manually.