generally speaking, no, not really. it depends on how much you trust the maintainers of the repositories. i dont trust nokia much, so im a bit cautious about upgrading, but i still install the upgrades unless theres damn good reason not to, and there hasnt been yet. IMO, you shouldnt have a repo installed that youre afraid to do apt-get upgrade with. for unstable repos, you should enable them, upgrade carefully and judiciously, and disable them, if you want to have some semblance of stability. anyway, do what you feel. it could fix the problem, or give you cancer.