Once the wort is chilled to below 120 F or so, I can't see any problems with stirring, even stirring vigorously. Before then, stir, but stir gently.
The only reason to not stir your wort is to avoid hot side aeration, but once you're at a temperature where that isn't a factor, I don't think it will be a problem to stir vigorously since you're just going to be aerating your wort anyway before you pitch your yeast.
If you have an immersion chiller, stirring helps a lot, since it helps push hot wort over the cool chiller coils. Monitoring temperature as the wort chills, I've seen huge temperature drops (like 5-10 F over 1 minute) stirring an using an immersion chiller.