One problem that crops up, besides those mentioned above, is encoding problems when attached to an email. This can be the result of teh settings used by an end user or a dial up service. It usually occors on pc to mac and resul;ts in no open or gibberish when yu open. The easiest way around this is to ask the people to zip the ai thing, Zip files will open with a normanl double click on osx since zip is now included in the os.
As Itchbug said, you're probably best off asking people to outline the fonts. You also might be best asking them to send you eps (with fonts outlined). It will open right up in AI and be easily workable, if necessary.
Using OSX 10.3.9 on a G4