I don't think I've ever seen aptitude ponder an upgrade for more than a minute, if that, so I'd definitely kill it and start over.
If you haven't already done so,
aptitude install aptitude dpkg is usually a good place to start, so that you can be sure the bulk of the upgrade will be handled by the best available tools. This step alone may fix whatever is causing your aptitude to go off into space.
If that doesn't do it, I'd take a look at the list of packages available for upgrade and start manually doing a couple at a time until I either discover the cause of the problem or things get into a state where
aptitude safe-upgrade is able to handle the rest.