Here's an easy way of reducing the file sizes of files saved from Illustrator: hide everything before you save the file! For example, I've got a 2MB file that reduces to 720KB when everything onscreen is hidden first. The amount the reduction varies between .eps & .ai files.
[robg adds: I don't have Illustrator to test this with, so I asked a friend about it. He confirmed that it works, but that you also then lose the previews normally associated with these files. Without previews, placement in another application (such as InDesign) is quite difficult, as you can't see what you're placing. Apparently, you'll see a warning to this effect if you save with everything hidden.]
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