The karma does have reliability problems. It's not just fanboys. It's a serious problem. Check riovolution.com. When I got mine, I was strongly advised to get an extended warranty. This is because Rio's support is awful awful awful and takes a long time. Furthermore, because Rio is so awful, there's a whole extended dialogue going on in those forums about "hitting" the karma to dislodge a locked hard drive as a last resort before sending it to satan, aka rio support.
Aside from potential hard drive failing, the unit itself occasionally has to be reformatted. Sometimes it will seem like a hard drive problem but is actually just due for a reformat. I haven't reformatted mine for a while, so on some songs it just crashes for no apparent reason. Really frustrating, because it takes some effort to get a paper clip and push the embedded reset button.
The unit also appears to be a dead model. That is, no more firmwares. So you'll never get universal mass storage, for example.
The sound quality is nice, and it plays Ogg and FLAC. The interface is 2nd to the iPod of the ones I have tried (zen, iriver, archos, ipod, karma). For the price, it's a good deal, but definitely try to get an extended warranty.