Documenting a hack I just figured out, b/c lots of the internet seems like they don't know about it.
So, PDF is a funny format, and Acrobat is a weird program for manipulating PDFs. One quirk is that, when you crop pages in Acrobat, it doesn't actually remove the page, it just adjusts the viewing area. On the one hand, this means you can later un-crop the page, but on the other, if your objective was to remove a bunch of extraneous crap to reduce the filesize (like, say, if you're then inserting the image into a document you intend to peddle to people on dial-up or other bandwidth-limited connections), this is not helpful.
The solution, of course, is to print the damn thing (which I figured out when messing around with the Print settings, to see whether a real printer would print the cropped or uncropped version.)
1. Open your cropped document, and go to File->Print. A dialogue box will come up.
2. Select 'Adobe PDF' from the list of Printers. Check the Properties; if "Do not send fonts to 'Adobe PDF'" is checked, un-check it.
3. Under Page Scaling, select 'Fit to Printer Margins'.
4. Click 'Ok'. It will prompt you for a filename and location.
5. Distiller will inform you when the job is finished, and open the new file for your perusal.
That's it, apparently. One potential drawback is that, unless you choose the paper size to be otherwise under Adobe PDF->Properties, the new page size will be 8.5"x11", but vector graphics are meant for scaling, hey?