I have seen/heard several questions about what type of headset to use for skyping on MacBooks over the last few days. Here are my suggestions:
USB headset: Since MacBooks do not come with a separate microphone input (only line level input), regular PC headsets with two mini-jack cables won’t work. I have good experience using USB headsets from Logitech. I have a couple of 250s, but since one of them broke during travel I also got a more durable H555. The latter is nice, since the actual headset can be physically removed from the USB sound card (a small dongle). This means that the sound card can be used with a different headset (or microphone). As such, it serves the same purpose as a small dedicated sound card like the iMic.
iPhone headset: It was only fairly recently that I discovered that newer MacBooks sport a 4-pin minijack connector. A regular stereo minijack has three pins (2 channels + ground), while the 4-pin connectors can also carry a microphone signal. This is the type of connector that is used in the iPhone headsets, which also means that your favourite iPhone headset can be used for skyping on the MacBook. After I discovered this I have no longer bothered bringing my USB headset around when travelling.
Built-in microphone: My experience is also that the built-in microphone and speakers on the MacBook actually work very well for skyping. I have had remarkably few feedback issues with my latest MacBook, so they have done some smart engineering to remove feedback problems in different parts of the chain. The only problem is that the microphone tends to pick up key strokes etc. very easily, so if you want to use your computer while skyping it is not the best way of doing things.
Conference microphone: When using Skype for more conference type of calls, i.e. where several people are supposed to be picked up, I use a small conference microphone ATR97 from Audio-Technica to get a better result. This I connect to the USB dongle of the Logitech H555 mentioned above, or my iMic. The only negative thing about the ATR97 is that I tend to forget to turn it off after use, so that the battery drains out.
Professional microphones: Of course, for the best sound quality it is possible to use a larger sound card and high quality microphone also for skyping. In my office I currently have a AKG GN 30 swan neck microphone connected to a Alesis MultiMix 4 USB mixer. The mixer plugs directly into the MacBook, and also gives access to simple adjustments of the frequency bands.
All in all, there are a great many different ways of getting sound into your computer, dependent on the situation, the quality needed and how much gear you want to carry around.