I'm Working in Plone 4.1 and I'm just curious to know the difference between Products.CMFPlone.interfaces.IPloneSiteRoot and Products.CMFCore.interfaces.ISiteRoot. If I want to register a zope-3 style view, to which one should I register it?
An IPloneSiteRoot is a specific kind of ISiteRoot. IPloneSiteRoot is provided by the root of a Plone site, whereas ISiteRoot is provided by any CMF portal. If your product is only intended to work in Plone, then it doesn't really matter which interface you use. If you want it to be usable with other CMF-based applications, then use ISiteRoot.
Frankly, I usually go with ISiteRoot just because it's shorter to type. :)