I have iphoto...does aperture do anything that iphoto doesn't? How does it compare to photoshop elements?

Can you work with RAW files in iPhoto? Actually, if OS X displays natively, then the answer to that is probably yes.
Does iPhoto do highlight recovery? Let you see the histogram of the image? Give you total control over full colour management? Does iPhoto give you spot removal tools? Let you selectively adjust certain colours without blowing out skin tones?

I'm just knocking these out from the top of my head as I don't use Aperture.

Mark

I use Aperture, and it is a major step up from iPhoto. I actually chose Aperture over Lightroom for the integration into MobileMe and uploading to the gallery and stuff.

Yes, iPhoto handles RAW (it's a function of the OS), and gives you some relatively basic adjustments. In short, it'll probably do everything you want. You can get plug-ins to let you manage uploads to Flickr and Facebook and so on.

But, if you want to start working with photos on an industrial (professional) scale, consider this: iPhoto is destructive editing. It creates a copy every time you make an adjustment, so you can return to the original if you cock it up. That's a full resolution copy,a full bitmap copy of your image. I know hard drive space is cheap, but that's a lot of space taken up if you want to try out variations on your original.

Aperture and Lightroom are both non-destructive management and editing software. You load up your RAW, it's converted by the software (arguments can be made in favour of either software as to which is better at this). Now, when you make exposure/contrast/colour/crop/rotation/sharpness adjustments, you see the result in the software, but the original file remains untouched. A sidecar file is created which has the instructions on how to replicate the changes you've made.

At any time, you can turn off the crop instruction, and it's done. No need to retrieve an original copy from its archive, no need for you to then recreate the other adjustments you've made. I often have multiple versions of an image, in various states of adjustment, but the software only keeps the one original master image at all times.

I'm not sure if more recent versions of iPhoto allow you to create and use different libraries, but I know Aperture and Lightroom do - a lot of pros set up specific libraries for their clients, and switch between them. It makes it a whole lot easier to manage the images, and a lot easier to back them up, too.

What I'm trying to say in amongst all this waffle is that if you are serious about your photography, consider moving up from iPhoto to something stronger, and consider it before your library gets out of hand.

Thanks Heather, I'm reading you loud and clear! It has given me something to think about - it isn't hideously expensive either.

That is standard for iPhoto these days, no plug-ins needed - it "just works".

Thanks Dave. I knew there was some of that stuff in the latest versions, but wasn't sure what. I'm still on iPhoto 6, where social networking was still a thing of the future.

Note that some 3rd Party plug-ins for Aperture go “destructive” - that is they create a TIFF of the image you are going to apply the filter to and work on that. At this point, cops, and other adjustments are fixed for that version of the photo. You do, of course, have your original as well.

I remembered this point when I was in bed, about 20 minutes after making my first comment above.
I don't use iPhoto at all so I can't really make any comparison between it and either Aperture or Lr.

Mark