IMF in Exchange 2007 is more configurable than in Exchange 2003, but I find it more cumbersome than GFI Mail Essentials, which I love.
For this particular Exchange 2007 server (via SBS 2008), I had users complaining about Microsoft and Facebook spam. Since the IMF updates were not adjusting the content filtering to adjust for these messages, I decided to add black lists. I have hated black lists for years, as I occasionally find myself on them and it's a bitch getting off of them - but conceptually, if the blacklist is accurate with no false positives, it should be a very good tools.
OF NOTE - you should limit your number of blacklists to 3. See this post for more information
To configure it, I opened up Exchange Management Console -> Organization Configuration -> Hub Transport and went to the anti-spam tab. I went into IP block list providers and added these blacklists:
Here are some others I could have added: