[thesilentdrummer]

It depends on the kind of music. For example, orchestral or choral music uses pushes and pulls very liberally (especially a Capella chamber choirs) to portray emotion. But since I am pretty sure thats not what you are talking about, usually solo-type pieces are good for liberal pushes and pulls. See billy Joel's "And So It Goes" for a real world example. However, in most full-band applications apart from what Richiebee said, one of the most common and useful tempo changes is to double or half the starting tempo. I believe Rush Halves "YYZ" in the middle of the song, and Lynyrd Skynyrd's "Free Bird" doubles the tempo for the fast part and guitar solos.

I would really avoid speedups of more than 5 BPM (that are not a double) over the course of the song. Songs tend to get out of control when the keep snowballing.