Not strictly access rules but I have just successfully implemented the

appnote re Blocking Browser Ads with BM and I was wondering how big
the
hosts file can get on the server before problems start (if at all?)
For
example, the example ad-ware list I downloaded today has 16,000
entries in
it. This is for BM3.7 running on NW6 all fully patched.

Cheers
Andrew