I think I replied to your post over on another forum. I have done a lot of boat towing over the years with my pickup trucks.
The key thing with towing a 3000 pound boat with an Outback will be to have the tongue weight set-up correctly. Boats generally have tongue weights of 5-7%, as compared to travel trailers which are typically 10% or more.
5-7% of 3000 is only 150-210 pounds, you can measure this with a bathroom scale, and these figures are within the Outbacks suggested tongue weight.
I would get your boat weighed on a certified scale (like at a truck stop) to make sure that it really does weigh only 3000 pounds all in. Additionally, I would add surge brakes to your trailer, you can get the parts at http://www.championtrailers.com/.
Good luck and let us now how you make out!