Thank you for your post, and I apologize for the late reply.
I am unable to replicate the problem. This is what I have done:
1. On a MacBook Pro running Mac OS X 10.6.8, I launch FileMaker Pro 10.0v3, open a database file, turn on Network Sharing, and then launch Safari.
2. On an iMac running Mac OS X 10.7.2, I launch FileMaker Pro 10.0v3, and access the hosted file on the MacBook Pro.
3. I then launch Pages, and start writing and writing. There is no change in performance over the next ten minutes.
Let me know what I'm doing differently than you. Also, since so much time has elapsed, if you have found any solution, please post here so others can benefit.