Personally, I've never been a big fan of extended warranties. They are of course like an insurance policy where most people never get their money back...to offset the cost of those few that do have major problems, plus some left to cover their admin expenses and profits. They also seem a bit pricey, considering they want to get your money now...not 3 years from now when the bumper to bumper expires, or 5 years for the power train.
I put 80,000 miles on my last Subie and never had a problem (of course that doesn't mean I won't this time) but I think you will find most people have had a low frequency of repair with Subaru. (Now if I bought a VW, I'd seriously consider it!)
If you are one of those unfortunate people who always seems to be the victim of auro repair scams and your local service department has a poor reputation, I MIGHT consider it, but only the one offered by Subaru, not a third party.
An extended warranty is a good investment if your subaru has a turbo. Turbos run hot and play havoc with engine parts over an extended period of time. I just took delivery of a 2005 XT Limited and am now shopping for an extended warranty. My dealer first quoted me $1500. for the Subaru 100k mile 7 year warranty. The dealer quickly lowered the price to $900 but I told him it was still too much. I'm hoping to come up with a better price. I'd be interested to hear from others who have purchased the subaru extended warranty.
If it is a new car that you purchased, I would check with your insurance company. The company that I have my autos insured with offers an extended warranty 7yr/100K for just about $6.00 a month. The deductible is $250, but it covers everything. When you put a claim in against this service it goes in as a non-incidental, meaning that it does not cause your rates to go up.
Since dealers are few and far between out here (3 dealers in the Phoenix area, with 3.5 million people), my dealer uses JM&A Group (http://www.jmagroup.com), which means all I have to do is call an 800-number to get a service station in my part of town that participates in this program (most AAA stations are eligible, as I understand it).
JM&A is highly rated by JD Power, and I believe was started by a Toyota dealer. I paid $1135 for a 7 year/100k mile warranty that covers virtually everything ($0 deductible). I figure that'll cover one bad transmission problem or a couple of other similar expenses, at least.