crop in illustrator

From klf:
Something for mat-illustrator-labor wot I just learned here (http://forums.adobe.com/thread/319423):

You know how you can crop things really easily in Photoshop but not in Illustrator?  This is a huge pain for figures with a lot of white space that you want to get rid of before submitting the figures for publication (e.g., for Matlab figures imported into Illustrator).  Here's a workaround in Illustrator that'll let you do what cropping does.

1. Open your big figure.  This figure includes some stuff you want to keep (e.g., data) and some stuff you want to get rid of (e.g., white space).
2. Create a shape on top of the figure the size and shape of the area you'd like to crop.  E.g., a rectangle.  Place it right over the stuff you want to keep.
3. Color that rectangle some color (e.g., white).  Doesn't matter what color.  Just make it something you can see.
4. Use the transparency palette to set the opacity of the rectangle to 0%.
5. Select the rectangle and the underlying figure.
6. Click on Object > Flatten transparency.  (Use 100% vector on the quality slider, and make sure the "Preserve alpha channel" box is unchecked.)
7. Ungroup the result.
8. Click on the things outside the rectangle and delete them.  Done!