@tuesday242 You should always backup. Aperture doesn’t claim that your photos are “unloseable”, but that editing images doesn’t destroy the original, raw image straight from the camera. Aperture maintains multiple copies of the same file, one being the original, which the application won’t let you edit.
I definitely like Aperture, although I don’t use it much anymore since I mostly use a MacBook. My biggest complaint is that it uses the 3D rendering engine in Mac OS X for the editing mode, so it runs like a slideshow on my MacBook’s worthless Intel GMA950 graphics processor. Comparable products, like Lightroom, run just fine on the same GPU.
The interface is much more straightforward than anything else I’ve used. I’m trigger happy—I take lots of successive shots of the same scene, so being able to quickly run through all my images and flag the keepers without deleting the others is great.
Contrary to my previous comment about performance, I’m generally very pleased with Aperture’s ability to let me fly through a massive library of RAW format images without too much slow down. Doing so using, say, Windows Explorer, can get frustrating for large volumes.