Does it block too? Or does the water just evaporate right off the fibers as if nothing happened? Acrylic is plastic right?
I think that you can attempt to block it but it probably won't stay in its blocked state.
Is there any way to make it keep its shape?
I've read that most acrylics don't require blocking. If you like the shape it has when you've finished knitting it, then don't block.
I've tried wet blocking (no steam) acrylic, but to no avail. What is the garment? If it's a sweater, then you might be happy with it when you seam it anyway. If it's a scarf, you may want to try blocking.
Generally people find that acrylic is nicer after a run through the wash. It redistributes the tension in the piece so that it's more even. This is bit helpful if things aren't quite the shape you want.
Acrylic doesn't block. When you put it in the washer it stretches, when you dry it, it goes back to its original size. Like Aidan said, it may make it look nicer.
When I use acrylic and I have the stockinete stich curly edge syndrome on something like a scarf I just submerge that sucker in water for like a half an hour then take it hour and wring out in a towel then lay it flat on something like a towel and pin it down and keep ith that way till it dries. Its not perfect but it doesn't curl so much. I use this method with TLC kinds of acrylic. Other kinds of acrylic may act differently.