raw water cooling system flush out

[TwinFin]

A friend of mine just had a fresh water flush kit installed on his Volvo Penta Diesel (stern drive set-up) engine (pic shown here). This re-sparked my curiosity/paranoia about our raw water cooling systems. Have any of you guys switched over to fresh water flush out plumbing? What experiences have other members of this board had with their heat exchangers and the rest of the raw water cooling system after many years of ownership? What components are you replacing and how often?

I noticed that VP has a corrosion prevention flush kit listed as an accessory. Click on the accessory catalog link once the page loads up.

http://www.volvo.com/volvopenta/na/en-us/partsservice/marine+parts/marine+parts.htm