Here is a quote from our Company Ops Manual (Canadian domestic carrier):
Carbon dioxide solid (dry ice), in quantities not exceeding 2 kg (4.4 lbs) per passenger when used to pack perishables not subject to these regulations in carry0on baggage provided the package permits the release of carbon dioxide gas. See note 2.
Note 2: Operator approval required for checked baggage only.
Permitted in or as carry-on baggage - YES
Permitted in or as checked baggage - YES
The approval of the operator is required - YES
The PIC must be informed of the location - NO
My book says nothing about the restrictions for checked baggage and fortunately as flight crew we do not deal with dangerous goods directly. This is handled by our cargo and check-in agents.
Hope this helps a bit.
Cheers
Canuck