Car acceleration-why is is so slow?

I have a '98 Subaru impreza outback/sport. It isnt exactly made to speed away like my old Impreza sedan, but i will be trying to p someone and accelerate on the interstate, i'll floor it and i might as well be giving it a little gas at a time cause it doesn't shift up or accelerate fast at all. My boyfriend, who is not used to driving the car, almost collided with someone the other day because he tried to p and accelerate (he had what looked like PLENTY of time to do this) and it just wasn't picking up speed. What is the problem and is it a problem? Is it just the way the car is?