Depend on which type of site you are planning to use it. Personally I prefer to use it on my MS when I have average metrics.
Never use it in obscure sites, BH sites, or sites that a footprint should not be left. I prefer to use other metric sites like mixpanel or clicky.
Also I never use it in starting sites with low level of visitors.
But I don't find huge evidences that support the fact that it could damage your rankings for trustworthy sites. Just always have in mind that the G identifier may serve to connect the dots to identify a possible network from your own. But other than that I feel that it can provide a huge value, that might cost a lot with other solutions.