As far as the photostream issues, try turning off one of your devices while trying to get it to work with the other, and see if you can narrow it down to either the iphone or the ipad. If it's not one of those, are you trying to stream over wifi or 3/4g? Reboot the router, and try it out. How old is your router? The other thing I would be curious about is your ram, but only if it's locking up when using other programs. There are free ram test utilities out there, as well as stress tests that would let you know if a part of your mac is failing. Being that you're using 3 apple products in conjunction, I would steer away from it being a software issue, and lean more to the side of it being a hardware issue, especially if it's a problem that is not easily googleable.