Being left-handed excludes me from enjoying most of the ergonomic mice that many righties enjoy. I have to settle for something ambidextrous, or a track pad. When I first bought my iMac I immediately sold the magic mouse - tried it for a week and just couldn't get into using it. I bought a track pad because my previous mac, a MBP, had one and I loved it. But... I ended up taking it back as well, because I couldn't justify $70 for it.
I've gone back and forth between 3rd party keyboards and the Apple ones, but ended up with an Apple wired keyboard. I really like the chicklet feel of their keyboards - it feels crisp - but always hated the bluetooth delay of a BT keyboard. That initial tap to wake it up, I could never discern whether or not it was going to pick it up or not, so I almost always had to retype my passwords twice, and it got annoying. There's a few times when I sort of wish I had a slightly thicker keyboard, but for the most part I really enjoy it.
As for the mouse... I ended up with another magic mouse after buying a 2nd iMac and decided to give it a second chance. I actually run with 2 mice: a wired Razer mouse for gaming (it's quite old and I'll probably replace it in the next year or two) and then the magic mouse for casual use. With the magic mouse, I like the gestures and the easy swiping when using Aperture and such; makes horizontal scrolling really easy. I don't like that sometimes gestures are inadvertently triggered and I lose focus on what I was doing because the mouse false-positive'd on my finger hovering just over the mouse. So it's hit and miss. I've gotten to where I move back and forth between the two mice rather seamlessly. It does require that I re-learn how I hold the mouse since it's smaller and more low profile, and sometimes it's gratifying to switch back to the razer and have a full-sized mouse in my hand that I can palm.
If I could pick up a track pad for inexpensive, or trade someone a track pad for the magic mouse, I think I would. I'd use the track pad for casual use and the wired mouse for gaming or when I just miss having a mouse. Either way I don't think I'd be happy settling for just one or the other, and there's really no need to.