There is nothing wrong with the iPhone geotagging. (see Jerakeen's post earlier in this thread) The wrong-hemisphere problem only occurs when you import the photo through iPhoto on your mac, AND THEN edit the photo somehow (crop it, for example, etc.). iPhoto then strips part of the EXIF data so that the East and West, North and South identifiers are removed (leaving it unclear if the photo was taken at 118 deg West, or 118 deg East, for example).
To avoid this, import to your mac using image capture instead of iPhoto. You can then import the photo into iPhoto if you like, but as soon as you edit the photo, the lat/lon references (not the values, just the indicators that tell whether the number is E or W of the prime meridian, or N or S of the equator) are stripped. This bug has been with iPhoto for a long time. (see this thread on flickr from over a year ago:
http://www.flickr.com/groups/geotagging/discuss/72157600040087961/) Maybe now that it's getting renewed attention from iphone users, apple will finally fix it. Geotagging photos has been a niche interest up to now, but since the iphone does it automatically, there might be enough squeaky wheels to get Apple to finally fix iphoto.