I, like many others, would probably advise you wait. I swap between iPhones and WP7 devices, liking them both for their own merits and differences.
One of the things I do find annoying as a Mac owner though is that any DRM content you have in iTunes is not going to sync and work on your WP device. That's fine for most music bought since Apple stripped off the DRM, but not so great for any older song content, or for films and TV programmes.
By the way, there are Office-compatible programmes for iOS devices that work with cloud services such as SkyDrive, Dropbox etc. That need not put you off getting an iPhone. But like any mobile device (including the Office apps on WP7), there are going to be features not available in the mobile versions that are available in the desktop counterparts, so it's worth investigating that side of things further.
As for the camera - check out lots of photos that people take if this is important to you - Flickr's Camera Finder is useful for that. Mere specifications never tell the whole story, and a lot of the quality of photos comes from the in-phone processing that goes on. For example, the photos from my Lumia 800 aren't quite as good as those from my former phone, the iPhone 4s, despite them both being 8mp devices with decent lenses - in the case of the Lumia, a branded lens at that.
Of course, that would involve waiting a little while for people to start posting in substantial numbers to Flickr, but hey, the Lumia 920 may drop a bit in price in the meantime, you never know.
Either way, iPhone 5 or Lumia 920, they'll both be great devices and I'm jealous you get to have either