On iPad or iPhone, I take a snapshot of the screen looking at the screen sideway, but the snapshot is taken to be in Portrait mode? On iPad or iPhone, I take a snapshot of the screen looking at the screen sideway (Landscape mode), but the snapshot is taken to be in Portrait mode?  So if I send this photo to a friend or post it on Facebook, it will be 90 degree off... 

(I mean taking a snapshot by pressing the Power and Menu button at the same time)

Any fix or hack to make it work better?  (this also looks like a bug that might be able to go into future release of iOS)

I can upload it to the computer and use the computer to turn it 90 degree... but what if there isn't a computer around?
You should be able to rotate images imported from a camera in iOS' Photos, so the functionality is there. For some reason it's not enabled for synced images or screenshots.

Instead of using a computer you can rotate images with an app providing the functionality. I think Myles also means this approach. Some free apps capable of image rotation:


PhotoPad
Adobe Photoshop Express