I agree that plateaus can by overcome by cross-training. Trying changing some aspects of yr workout. If you are currently doing step, try incorporating kickboxing or hi-lo or interval training. If you are doing crunches, try working the abs through core-stabilisation. The body will then have to adapt to the new challenges.
Variety is the key.
You don't have to make a drastic overhaul to yr current exercise regimen. Just some changes to some elements should bring about beneficial changes. Just my 2 cents worth. Collage Video, exclusively selling exercise videos since 1987. Full descriptions of 645 tapes.