I have been using Sennheiser headsets for a long time, for gaming, video conferencing, and general enjoyment. They have excellent audio quality, but — more importantly — I can comfortably wear mine for an entire day. The headset that I have (now discontinued) has dual 3.5 mm connector (one for the microphone, one for the headphones) at the end of a single cable, which I used to connect to my Mac using a USB adapter (which came included with the headset).
So I was more than a little disappointed when I got a shiny new 2013 iMac (27 inch) and found out that just having the USB adapter plugged in caused intermittent crashes. This really put a damper on my WoW experience productivity.
There are reports all over Apple’s support forums of other people having the same problem, with no solution offered. Other USB adapters are reportedly failing in the same way, which is why I was reluctant to try buying random adapters in hope that one of them works.
Then I realized that the audio port on the new iMac supports both input and output, at which point I bought an adapter that merges the two connectors from my headset into one connector on my iMac. No problems so far.