A usenet posting suggests that XS4ALL will provide a filtering service to their subscribers. The filter would consist of 5 levels. Ranging from fully open to 'fully' closed. The first will give you the possibility of running your own services at home, and the latter means you're only able to e.g. surf and e-mail (through the XS4ALL SMTP server).
The filters would give the basic/ignorant user the opportunity of preventing the spreading of malware and other stuff by default. The more tech savvy subscribers can remove the filter for running a bunch of services (webserver, ftp, mail, DNS, etc).
Definitely a good decision. I just hope that the other ISP's will do something similar, because most of the virus/malware/massmailing 'software' is running on PC's run by the average user. Totally ignorant of the malware running on their PC's.
Yet another 'thumbs up' for the quality provider of the Netherlands