What are the effects of rust?

[PoonTang]

So I was doing some maintenance on my return pump and discovered that the Stainless Steel holder for the ceramic seals had quite a lot of rust on it. Does anyone know what the effects of rust are on our tanks or have any personal experience with it? My tank is definitely having issues at the moment.

[apexifd]

http://www.advancedaquarist.com/2002/8/chemistry

[Aquattro]

I've always had rusty hose clamps and screws in my sumps, never a problem with it.