tend to pick up background noise, and they also don't have a lot of input gain. I have one, and it suits its purpose, but it can be frustrating.
If you're looking to reduce noise and have a higher quality input, I suggest you use a standard XLR microphone but use an XLR to USB cable. This way you'll get the high quality of the microphone input, but direct to hard disk audio with the USB cable.
That might not be the most popular answer, since it requires a little more investment on your part, but it is an option.
I recently wrote a post on my blog about it here:http://www.musictyro.com/choosing-usb-m ... 010/01/14/