Sony runs this deal fairly often, but now is the time to make use of it once again. If you buy one year of PlayStation Plus from now until March 4th, you'll get three months free.
Sony reports that last year PlayStation Plus had a combined savings of $2,472 if you add up all of the services, free games, PS Vita support, and the "Instant Game Collection." They also tease that there's more to come in 2013.
As someone who has been a "Plus" member since shortly after launch, I've been satisfied. Every since I got Sam & Max for free and paid for my subscription day one, I knew it was worth it.
PlayStation Plus [PlayStation Blog]