Do you guys use the spray-in expanding foam to seal up the wood window cases? I have 2x12's in the basement and 2x10's in the main floor, and I was wondering if it would cause problems to just use spray in foam to seal it up.

Thanks
Brian

spray away.. if you're concerned about movement, use the window and door expanding foam.. it doesn't go as far as the gaps & cracks filler, but is less likely to warp anything.  I've enough experience with the stuff now that I only use the gaps and cracks filler for around doors and windows, it's less costly... ohhh, but be careful because it can darn near move walls if you're not. 

A minimally expanding foam is safer to use in situations where the foam may cause movement.  That is what I would use in your situation.

Foam done slowly and carefully can be used to seal both doors and windows.  Be careful and apply in small stages if you don't have any unwanted experiences.  We use it on many jobs. 

I think the term "seal" here means air infiltration only, not water. Of course thats what the exterior finish is for anyway :-)

Good point Jim.  It does mean only air.