While I am far from an expert in access I can tell you that from my experience it seems best to have each users front end on their own hard drive - I know that it makes it more of a pain to update their forms but it seems to help speed up the database.
There have been other posts on this website that address these issues.
I have also experienced problems when I was in the same front end as one of the users of my database - At one time, I had all of the users front-ends on a network drive -
I did find it more helpful when each users front end was seperate for a few reasons - first, I could go into windows explorer and see who was in the database when I told them to get. Second, it makes updating easier.
Thanks