Yeah I too am facing the same problem of inverted photos when mailed or transfered to the pc. i suppose that this problem is occuring due to photo stream option in icloud. The bug in photo stream application is causing the same i suspect.
Just for once put photo stream off in your phone and then take photos and videos and try syncing them with the pc and it should work alright.
i also noticed that the videos taken with photo stream on appear inverted if played on a media player but only if they are played on quick time then sum times they appear normal but i myself am not much a fan of quick time that much.
But i consider putting photo stream off is like cutting the icloud feature and always hav to transfer photo through cable quite headache . apple should come out with this bug fix in photo stream
atleast i can point out that cause it was the case on my iphone 4s.
I would like to know whether this is true for all iphones .
juss put photo stream off from icloud and check if what i am suspecting is true or not.
also i found that few photos transfered using when photo stream is on gives error saying problem with the file properties because of which the photos are not able to be rectified to a proper orientation.