If you know how to correctly use FileMaker to host the database for other users, there should be no major issues in getting this to work. But if by "Filesharing" you want to put a copy of your database into a shared directory and have different users open it directly, you risk damaging the file--and this is the case whether you have just Macs, just PCs or a mix of the two.
There are some differences in behavior between the two platforms but how you host the file and access the hosted database is the same on both systems. You open the file on the server using FileMaker Pro or FileMaker server and then all clients use Open Remote to find and open the database file thus hosted.
PC to mac differences: The same block of text takes a few more pixels of space on a PC than a Mac. Thus, you'll need to examine and adjust your layouts if you spot places where text is "clipped" or "wraps" in unexpected ways.
Printing from a mac provides a Percent scaling option not available on PCs.
On PC's you get a rather awful "FileMaker window inside an application window" look not found in Macs. Window thus can behave a bit differently--especially if your solution opens and closes a number of different windows when the user interacts with your database.
File Paths are different on PCs and Macs as a file path on a Mac starts with a volume name and starts with a drive letter on PCs. Thus parts of your database that rely on file paths--such as a container where files are inserted with "store a reference" can encounter issues that need modification before your solution is fully "cross platform" capable.
Wow, okay, thank you for going beyond my question and alerting me to these other issues! It's good to know that the sharing of the database using the network sharing option (I did not mean "file sharing") should work in a mixed environment. I heard that using network sharing is not ideal, and that using FMP server is highly recommended instead, but since there are less than 10 users, I hope this method of sharing will be fine.
If you are using FileMaker 12 or older it works quite well as long as you understand the limitations of that method. FileMaker 13 is more limited as it only supports half as many connections before you have to upgrade to using Server.
Again, good to know and thanks! Luckily we are on FMP12 (advanced).