Originally Posted by DoWBrewer
If you did get a little oxygen in your carboy, it won't hurt anything as long as you have yeast present. The yeast will take care of the oxygen.
That's not strictly true. As I understand it, yeast only consume oxygen during the lag phase, as they use it to metabolize sterols and replicate themselves to build up the necessary colony size to perform fermentation. Once they've finished multiplying and enter the main phase, oxygen uptake essentially ceases, and additional oxygen will oxidize the beer.