To the OP:
What is it you want your software to do, and is there something iPhoto does not do that you want it to?
The reason I ask is that I have seen people getting into underwater photography and want to use more complicated equipment or software without really knowing what they are getting themselves into. For example, on dive trips I spend 1-2 hours each evening dealing with camera gear, downloading photos and doing some light editing. After the trip I will spend an additional 2-12 hours (depending on how long the trip was, and how I liked my photos) doing additional editing, uploading to websites and choosing photos to print.
I use lightroom 4 for organizing and Photoshop 5 for editing. I shoot exclusively in RAW and each photo can take up anywhere for 15MB (original RAW) to 300MB (TIFF). For me iPhoto was nowhere near powerful enough, or fast enough to deal with images that large, but I still use it for organizing jpgs and videos that I am going to upload to my website. I used Aperture for awhile and never really liked it, just a personal thing, I like lightroom's organization and editing tools better.
If iPhoto is doing what you want right now, there is no reason to switch. You know how to use it, and it's free. I would wait to see what the Yosemite photo program is like before recommending a switch. If you think that you have no interest in spending as much time as I do (and I know people who spend much more time), I wouldn't recommend using the same software that I do.
A couple years ago I was working at Optical Ocean Sales, and took a phone call from someone who had been reading online about focal nodes, and virtual focusing, and ideal distances from the lens to the inside of the port. He wanted to order a new port extension because of what he read ($225 or so for 5mm difference). I asked if his lens was focusing with his current extension, and he said yes. I asked if his photos were sharp, and he said yes. I asked if his equipment works for what he is doing, why would he spend money on something that the internet said was better? He did not end up getting the extension.
Just because something works better for someone else, there is no reason to switch unless you feel like your equipment is not working for you.