Have you installed any third-party repositories and then it became slower? I wouldn't think about reinstalling/upgrading just yet. May be a minor glitch (and you may face major ones with a 3 week old release).
You shouldn't need to speed up the boot time on a healthy install. There's not a lot you can do in Linux anyhow. You could try switching off services that boot with your machine. I'm using Xubuntu and it's Setting>Sessions & Startup. In Ubuntu should be in settings somewhere. Have a look there now and see if that is your problem. Because you are getting the repo error I'd say more likely related to that and that should be fixable.
You obviously have a problem since install if you have been experiencing this since then.
Could you also post your sources.list by opening a terminal and:
Post the output back here, please.