Panbo.com is running a piece on AIS Class B filtering from displays such as Coastal Explorer and other tracking systems.
I spoke to a sales guy from Rose Point a year ago. He said the first feature request they got after adding AIS tracking was a filter for Class B.
Personally, I think it is crazy. We shouldn't have to have somebody in a small vessel die before this attitude is legislated away.
What we need is intelligent filtering based on speed of approach or time to collision. If the display is unreadable due to too much data, then there are known techniques in the user interface world to fix it.
If you read the accident report of the 2007 Ouzo Incident where a small yacht was run down by a ferry in the English Channel, you will begin to understand how important Class B transponders are to small boat safety. The small yacht did not use their radio effectively, visibility was poor and radar reflectors were useless.
AIS might have saved lives if a Class B transponder were installed on Ouzo and no Class B filter was in use by the ferry. It is also a common issue in operational software that features such as a filter are dangerous because the operator may forget to disable it after leaving congested waters.
I personally had an encounter with two freighters off of San Diego in poor visibility. I would not like to be in a situation where large ships maneuver to avoid each other and run over me because I am not visible.
The Ouzo case was also covered in depth by Practical Boat Owner.
I should also say that I purchased Coastal Explorer, because I think it is very good software separate from this filter issue.