I have just purchased Aperture and woukd like opinions on the pro's and con's of rerplaceing iPhoto completely with Aperture?
Aperture and iPhoto are designed as tools for the same tasks; Aperture is the more elaborate application, that will give you more options and more control, a better raw fine tuning, and more advanced editing tools. It is more suitable for very large photo libraries and has better tools to design and organize your photo library. Only it will take more time to learn, what is possible and how to adapt Aperture to your needs.
But you do not have to jump right in - you can migrate gradually. Aperture and iPhoto can share their libraries. There is no need to ever abandon iPhoto. You can simply open your iPhoto Library in Aperture and get going. Aperture 3.3: Using a unified photo library with iPhoto and Aperture
And you want to do things that Aperture cannot do, e.g. print cards, open your Aperture library in iPhoto. Keep iPhoto around, see:
Keep iPhoto - It May Come in Handy!
Regards
Léonie