Or atleast how I oven formed acrylic. A few weeks ago I sent out a file (acrylic flatware) to Ponoko to be laser cut. These are the steps I took to form the flatware into usable shapes. It's very easy to do!

What you need:
Acrylic
Oven
Baking Sheet
Aluminum Foil
Timer
Felt - for handling the acrylic and to prevent scratches
Tools for forming

Tools for forming may include:
a Mold - any object/shape you can press the acrylic into to give it shape
mallet and/or a peen for shaping

Caution, Ive only tried this in an Electric Oven. I cant recommend for gas ovens.

Im forming the flatware and using 2 forks and 2 spoons I already have to shape my acrylic fork and spoon.

I also turned it into a video, you can watch that down below or click through the rest of the steps.

Step 1: Preheat Oven to 300 Degrees Fahrenheit

Simple enough.

Step 2: Unwrap the Acrylic From Its Protective Sheets

Easier said than done.

Step 3: Bake and Set the Timer

When oven is at 300, place the plastic on a piece of aluminum foil on the baking sheet. Set timer.

Time varies depending on thickness of the plastic. I heard 15 minutes for each 1/43 thickness was the rule of thumb.
My particular acrylic is 3mm (.123 or 3/253), I put it in for 5 minutes - worked great for my thickness.

Step 4: Remove From the Oven

The acrylic should be fairly malleable and will begin to cool rapidly.

Dont touch without the felt. If youre working larger, you will probably want leather safety gloves. The acrylic at this stage will take on any shape, including your finger prints.

The acrylic might stick to the foil. Gently rub it with any smooth object and it will pop right off.

Step 5: Forming

Immediately begin to form. When plastic is on the felt begin to push into the mold/form.

Press acrylic into place for about a minute, until the plastic is no longer moving.

Youre done.