brinked - 6:16 am on Sep 18, 2012 (gmt 0)
You should not have any negative long term effects from this. You might experience a temporary loss in rankings but they should be restored shortly.
I have a lot of experience with changing title tags and I try to avoid doing it but overall I have never really been hurt long term by it. And I have a site with thousands of indexed pages where at times I have changed them all at once.