Also, although this is unrelated to the crashing, make sure that you launch the photo from iPhoto into PSE by right / ctrl- clicking it and selecting edit in external editor (or doing this by double-click, if that's how you set it up). At least in my experience, if you drag the picture to the PSE dock icon, you will overwrite the original and not be able to revert to it.
Also, in relation to CanadaRAM's excellent suggestion, this issue only comes up when you make changes that "unflatten" the image by adding layers, etc. In general, if you take an image and do most of the things in the image, enhance and filter menus, it should default to re-save as JPG or whatever the original format was. I think rotate is a notable exception though -- because the rotate always acts on a layer, IIRC, meaning that you will always be forced to "unflatten" your image to do a rotate, and then you will have to flatten it to save a JPG.